<PAGE>   1
                                  UNITED STATES

                       SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549

                                    FORM 10-Q

       (Mark one)

          [X]      QUARTERLY REPORT UNDER SECTION 13 OR 15(d) OF THE
                   SECURITIES EXCHANGE ACT OF 1934

FOR THE QUARTERLY PERIOD ENDED, JUNE 30, 1999

                                       OR

          [ ]      TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF
                   THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from ____________ to ____________

COMMISSION FILE NO. 33-13437

                          DEL TACO INCOME PROPERTIES IV
                        a California limited partnership
             (Exact name of registrant as specified in its charter)

              CALIFORNIA                              33-0241855
    (State or other jurisdiction of                 (I.R.S. Employer
    incorporation or organization)               Identification Number)

           23041 AVENIDA DE LA CARLOTA, LAGUNA HILLS, CALIFORNIA 92653
               (Address of principal executive offices) (Zip Code)

                                 (949) 462-9300
              (Registrant's telephone number, including area code)

Indicate by check mark whether the registrant (1) has filed all reports required
to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during
the preceding 12 months (or for such shorter period that the registrant was
required to file such reports), and (2) has been subject to such filing
requirements for the past 90 days. Yes [X] No [ ]

<PAGE>   2
                                      INDEX

                          DEL TACO INCOME PROPERTIES IV

<TABLE>
<CAPTION>
PART I. FINANCIAL INFORMATION                                        PAGE NUMBER
-----------------------------                                        -----------
<S>                                                                  <C>
Item 1. Financial Statements and Supplementary Data

Balance Sheets at June 30, 1999 (Unaudited) and
     December 31, 1998                                                     3

Statements of Income for the three and six months ended
     June 30, 1999 and 1998 (Unaudited)                                    4

Statements of Cash Flows for the six months ended
     June 30, 1999 and 1998 (Unaudited)                                    5

Notes to Financial Statements                                              6

Item 2.  Management's Discussion and Analysis of
         Financial Condition and Results of Operations                     8

PART II. OTHER INFORMATION

Item 6.  Exhibits and Reports on Form 8-K                                 10

SIGNATURES                                                                11
</TABLE>


                                      -2-
<PAGE>   3
                          DEL TACO INCOME PROPERTIES IV

                                 BALANCE SHEETS

<TABLE>
<CAPTION>
                                                    JUNE 30,         DECEMBER 31,
                                                      1999               1998
                                                  ------------       ------------
                                                   (UNAUDITED)
<S>                                               <C>                <C>
                                     ASSETS

CURRENT ASSETS:
    Cash                                          $     90,032       $    101,404
    Receivable from General Partner (Note 4)            25,749            106,724
    Deposits                                               452                504
                                                  ------------       ------------
        Total current assets                           116,233            208,632
                                                  ------------       ------------
PROPERTY AND EQUIPMENT, AT COST:
    Land and improvements                            1,236,700          1,236,700
    Buildings and improvements                       1,289,860          1,289,860
    Machinery and equipment                            484,789            484,789
                                                  ------------       ------------
                                                     3,011,349          3,011,349
    Less--accumulated depreciation                     973,168            921,294
                                                  ------------       ------------
                                                     2,038,181          2,090,055
                                                  ------------       ------------
                                                  $  2,154,414       $  2,298,687
                                                  ============       ============

                        LIABILITIES AND PARTNERS' EQUITY

CURRENT LIABILITIES:
    Payable to Limited Partners                   $     19,151       $     18,684
    Accounts payable                                     5,040              5,271
                                                  ------------       ------------
        Total current liabilities                       24,191             23,955
                                                  ------------       ------------
OBLIGATION TO GENERAL PARTNER                          137,953            137,953
                                                  ------------       ------------
PARTNERS' EQUITY:
    Limited Partners                                 2,003,481          2,146,545
    General Partner-Del Taco, Inc.                     (11,211)            (9,766)
                                                  ------------       ------------
                                                     1,992,270          2,136,779
                                                  ------------       ------------
                                                  $  2,154,414       $  2,298,687
                                                  ============       ============
</TABLE>

                          The accompanying notes are an
                   integral part of these financial statements


                                      -3-
<PAGE>   4
                          DEL TACO INCOME PROPERTIES IV

                              STATEMENTS OF INCOME

                                   (UNAUDITED)

<TABLE>
<CAPTION>
                                        THREE MONTHS ENDED          SIX MONTHS ENDED
                                             JUNE 30,                    JUNE 30,
                                      ----------------------      ----------------------
                                        1999          1998          1999          1998
                                      --------      --------      --------      --------
<S>                                   <C>           <C>           <C>           <C>
REVENUES:
     Rent (Notes 3 and 4)             $ 76,347      $ 80,385      $153,360      $152,813
     Interest                              682           265         1,994           653
     Other                                  50           475           275           625
                                      --------      --------      --------      --------
                                        77,079        81,125       155,629       154,091
                                      --------      --------      --------      --------
EXPENSES:
     General and administrative          8,706         8,791        28,146        27,834
     Depreciation                       25,937        25,937        51,874        51,874
                                      --------      --------      --------      --------
                                        34,643        34,728        80,020        79,708
                                      --------      --------      --------      --------
         Net income                   $ 42,436      $ 46,397      $ 75,609      $ 74,383
                                      ========      ========      ========      ========
     Net income per limited
       partnership unit (Note 2)      $   0.25      $   0.28      $   0.45      $   0.45
                                      ========      ========      ========      ========
</TABLE>

                          The accompanying notes are an
                  integral part of these financial statements.


                                      -4-
<PAGE>   5
                          DEL TACO INCOME PROPERTIES IV

                            STATEMENTS OF CASH FLOWS

                                   (UNAUDITED)

<TABLE>
<CAPTION>
                                                                 SIX MONTHS ENDED
                                                                     JUNE 30,
                                                            ---------------------------
                                                               1999             1998
                                                            ----------       ----------
<S>                                                         <C>              <C>
CASH FLOWS FROM OPERATING ACTIVITIES:

Net income                                                  $   75,609       $   74,383
Adjustments to reconcile net income to net
   cash provided by operating activities:
     Depreciation                                               51,874           51,874
     Decrease in receivable from
        General Partner                                         80,975           37,363
     Decrease (increase) in deposits                                52             (312)
     Increase in accounts payable and
        payable to limited partners                                236           11,229
                                                            ----------       ----------
             Net cash provided by operating activities         208,746          174,537

CASH FLOWS FROM FINANCING ACTIVITIES:

Cash distributions to partners                                (220,118)        (156,544)
                                                            ----------       ----------
Net (decrease) increase in cash                                (11,372)          17,993

Beginning cash balance                                         101,404           75,411
                                                            ----------       ----------
Ending cash balance                                         $   90,032       $   93,404
                                                            ==========       ==========
</TABLE>


                          The accompanying notes are an
                  integral part of these financial statements.


                                      -5-
<PAGE>   6
                          DEL TACO INCOME PROPERTIES IV

                          NOTES TO FINANCIAL STATEMENTS

                                  JUNE 30, 1999

NOTE 1 - BASIS OF PRESENTATION

The accompanying financial statements, some of which are unaudited, have been
prepared in accordance with generally accepted accounting principles for interim
financial information and with the instructions to Form 10-Q and Article 10 of
Regulation S-X. Accordingly, they do not include all of the information and
footnotes required by generally accepted accounting principles for complete
financial statements and should therefore be read in conjunction with the
financial statements and notes thereto contained in the partnership's annual
report on Form 10-K for the year ended December 31, 1998. In the opinion of
management, all adjustments (consisting of normal recurring accruals) necessary
to present fairly the partnership's financial position at June 30, 1999, the
results of operations and cash flows for the six month periods ended June 30,
1999 and 1998 have been included. Operating results for the three and six months
ended June 30, 1999 are not necessarily indicative of the results that may be
expected for the year ending December 31, 1999.

NOTE 2 - NET INCOME PER LIMITED PARTNERSHIP UNIT

Net income per limited partnership unit is based upon the weighted average
number of units outstanding during the periods presented which amounted to
165,375 and 165,415 in 1999 and 1998, respectively.

Pursuant to the partnership agreement, annual partnership income or loss is
allocated one percent to the General Partner and 99 percent to the limited
partners. Partnership gains from any sale or refinancing will be allocated one
percent to the General Partner and 99 percent to the limited partners until
allocated gains and profits equal losses, distributions and syndication costs,
and until each class of limited partners receive their priority return as
defined in the partnership agreement. Additional gains will be allocated 12
percent to the General Partner and 88 percent to the limited partners.


                                      -6-
<PAGE>   7
                          DEL TACO INCOME PROPERTIES IV

                    NOTES TO FINANCIAL STATEMENTS - CONTINUED

                                  JUNE 30, 1999

NOTE 3 - LEASING ACTIVITIES

The partnership leases certain properties for operation of restaurants to Del
Taco, Inc. on a triple net basis. The leases are for terms of 32 years
commencing with the completion of the restaurant facility located on each
property and require monthly rentals equal to 12 percent of the gross sales of
the restaurants. There is no minimum rental under any of the Leases.

For the three months ended June 30, 1999, the two restaurants operated by Del
Taco, for which the partnership is the lessor, had combined, unaudited sales of
$414,256 and net income of $20,878 as compared to $419,908 and $27,633
respectively, for the corresponding period in 1998. Net income by restaurant
includes charges for general and administrative expenses incurred in connection
with supervision of restaurant operations and interest expense. For the three
months ended June 30, 1999, the one restaurant operated by a Del Taco
franchisee, for which the partnership is the lessor, had unaudited sales of
$221,967 as compared with $249,962 during the same period in 1998.

For the six months ended June 30, 1999, the two restaurants operated by Del
Taco, for which the partnership is the lessor, had combined, unaudited sales of
$823,824 and net income of $53,481 as compared to $807,407 and $46,849
respectively, for the corresponding period in 1998. For the six months ended
June 30, 1999, the one restaurant operated by a Del Taco franchisee, for which
the partnership is the lessor, had unaudited sales of $454,183 as compared with
$466,031 during the same period in 1998.

NOTE 4 - TRANSACTIONS WITH DEL TACO

The receivable from the General Partner consists primarily of rent accrued for
the month of June. The June rent was collected on July 13, 1999.

Del Taco, Inc. serves in the capacity of general partner in other partnerships
which are engaged in the business of operating restaurants, and three other
partnerships which were formed for the purpose of acquiring real property in
California for construction of Mexican-American restaurants for lease under
long-term agreements to Del Taco, Inc. for operation under the Del Taco trade
name.

In addition, see Note 5 with respect to certain distributions to the General
Partner.

NOTE 5 - DISTRIBUTIONS

On July 13, 1999, a distribution to the limited partners of $65,221 or
approximately $.39 per limited partnership unit, was approved. Such distribution
was paid July 15, 1999. The General Partner also received a distribution of $659
with respect to its 1% partnership interest.


                                      -7-
<PAGE>   8
ITEM 2. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
        OF OPERATIONS

Liquidity and Capital Resources

The partnership offered limited partnership units for sale between June 1987 and
June 1988. 14.5% of the $4.135 million raised through sale of limited
partnership units was used to pay commissions to brokers and to reimburse the
General Partner for offering costs incurred. Approximately $3 million of the
remaining funds were used to acquire sites and build three restaurants. In
February of 1992, approximately $442,000 raised during the offering but not
required to acquire sites and build restaurants was distributed to the limited
partners.

The three restaurants leased to Del Taco make up almost all of the income
producing assets of the partnership. Therefore, the business of the partnership
is almost entirely dependent on the success of the Del Taco trade name
restaurants that lease the properties. The success of the restaurants is
dependent on a large variety of factors, including, but not limited to, consumer
demand and preference for fast food, in general, and for Mexican-American food
in particular.

Results of Operations

The partnership owns three properties that are under long-term lease to Del Taco
for restaurant operations (Del Taco, in turn, has sub-leased one of the
restaurants to a Del Taco franchisee).

The following table sets forth rental revenue earned by restaurant for the year:

<TABLE>
<CAPTION>
                                          THREE MONTHS ENDED           SIX MONTHS ENDED
                                               JUNE 30,                    JUNE 30,
                                        ----------------------      ----------------------
                                          1999          1998          1999          1998
                                        --------      --------      --------      --------
<S>                                     <C>           <C>           <C>           <C>
Orangethorpe Ave., Placentia, CA        $ 33,909      $ 34,347      $ 67,546      $ 66,022
Lakeshore Drive, Lake Elsinore, CA        26,636        29,996        54,501        55,924
Highland Ave., San Bernardino, CA         15,802        16,042        31,313        30,867
                                        --------      --------      --------      --------
            Total                       $ 76,347      $ 80,385      $153,360      $152,813
                                        ========      ========      ========      ========
</TABLE>

The partnership receives rental revenues equal to 12 percent of gross sales from
the restaurants. The partnership earned rental revenue of $76,347 during the
three month period ended June 30, 1999, which represents a decrease of $4,038
from 1998. The partnership earned rental revenue of $153,360 during the six
month period ended June 30, 1999, which represents an increase of $547 from
1998. The changes in rental revenue between 1999 and 1998 are directly
attributable to changes in sales levels at the restaurants under lease.


                                      -8-
<PAGE>   9
ITEM 2. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
        OF OPERATIONS - CONTINUED

The following table breaks down general and administrative expenses by type of
expense:

                               Percentage of Total
                        General & Administrative Expense

<TABLE>
<CAPTION>
                                                            Six Months Ended
                                                                June 30,
                                                         ----------------------
                                                          1999            1998
                                                         ------          ------
<S>                                                      <C>             <C>
Accounting fees                                           71.61%          71.66%
Distribution of
  information to
  limited partners                                        28.39           28.34
                                                         ------          ------
                                                         100.00%         100.00%
                                                         ======          ======
</TABLE>

General and administrative costs for the six month period ended June 30,
increased from 1998 to 1999 due to increased costs for accounting and income tax
return preparation.

For the three months ended June 30, 1999, net income decreased by $3,961 from
1998 to 1999 due to the decrease in revenues of $4,046 which was partially
offset by the $85 decrease in general and administrative expenses. For the six
months ended June 30, 1999, net income increased by $1,226 from 1998 to 1999 due
to the increase in revenues of $1,538 which was partially offset by the $312
increase in general and administrative expenses.

The General Partner does not believe the operations of the partnership will be
significantly impacted by the year 2000 software issue and does not believe the
year 2000 software issue will materially effect the partnerships operations,
financial position or cash flows.


                                      -9-
<PAGE>   10
PART II. OTHER INFORMATION

Item 6. Exhibits and Reports on Form 8-K

(a) Exhibit 27 -- Financial Data Schedule

(b) No reports on Form 8-K were filed during the six months ended June 30, 1999.


                                      -10-
<PAGE>   11
                                   SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the
Registrant has duly caused this report to be signed on its behalf by the
undersigned thereunto duly authorized.

                                       DEL TACO INCOME PROPERTIES IV
                                       (a California limited partnership)
                                       Registrant

                                       Del Taco, Inc.
                                       General Partner


Date: July 30, 1999                    /s/ Robert J. Terrano
                                       ----------------------------------------
                                       Robert J. Terrano
                                       Executive Vice President,
                                       Chief Financial Officer

Date: July 30, 1999                    /s/ C. Douglas Mitchell
                                       ----------------------------------------
                                       C. Douglas Mitchell
                                       Vice President and Corporate Controller


                                      -11-
<PAGE>   12
                                 EXHIBIT INDEX

<TABLE>
<CAPTION>
Exhibit
Number               Description
-------              -----------
<S>                  <C>
   27                Financial Data Schedule
</TABLE>