<PAGE>   1
 
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                                 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, MARCH 31, 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)
 
<TABLE>
<S>                                                          <C>
 
                         CALIFORNIA                                    33-0241855
              (STATE OR OTHER JURISDICTION OF                       (I.R.S. EMPLOYER
               INCORPORATION OR ORGANIZATION)                      IDENTIFICATION NO.)
 
   23041 AVENIDA DE LA CARLOTA, LAGUNA HILLS, CALIFORNIA                  92653
          (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES)                     (ZIP CODE)
</TABLE>
 
                                 (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  ___
 
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<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 March 31, 1999 (Unaudited) and
     December 31, 1998                                                                  3

Statements of Income for the three months ended
     March 31, 1999 and 1998 (Unaudited)                                                4

Statements of Cash Flows for the three months ended
     March 31, 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>

                                                                  MARCH 31          December 31
                                                                    1999                1998    
                                                                -----------         -----------
                                                                (UNAUDITED)
                                     ASSETS
<S>                                                             <C>                 <C>        
CURRENT ASSETS:
  Cash                                                          $   166,148         $   101,404
  Receivable from General Partner (Note 4)                           26,699             106,724
  Deposits                                                              478                 504
                                                                -----------         -----------
    Total current assets                                            193,325             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                                    947,231             921,294
                                                                -----------         -----------
                                                                  2,064,118           2,090,055
                                                                -----------         -----------

                                                                $ 2,257,443         $ 2,298,687
                                                                ===========         ===========


                        LIABILITIES AND PARTNERS' EQUITY

CURRENT LIABILITIES:
  Payable to Limited Partners                                   $    18,745         $    18,684
  Accounts Payable                                                    8,510               5,271
                                                                -----------         -----------
    Total current liabilities                                        27,255              23,955
                                                                -----------         -----------

OBLIGATION TO GENERAL PARTNER                                       137,953             137,953
                                                                -----------         -----------

PARTNERS' EQUITY:
  Limited Partners                                                2,102,446           2,146,545
  General Partner-Del Taco, Inc.                                    (10,211)             (9,766)
                                                                -----------         -----------
                                                                  2,092,235           2,136,779
                                                                -----------         -----------

                                                                $ 2,257,443         $ 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
                                            MARCH 31
                                      1999           1998 
                                    -------        -------
<S>                                 <C>            <C>    
REVENUES:
  Rent (Notes 3 and 4)              $77,014        $72,428
  Interest                            1,312            388
  Other                                 225            150
                                    -------        -------
                                     78,551         72,966
                                    -------        -------

EXPENSES:
  General and administrative         19,441         19,043
  Depreciation                       25,937         25,937
                                    -------        -------
                                     45,378         44,980
                                    -------        -------

Net income                          $33,173        $27,986
                                    =======        =======

Net income per limited
  partnership unit (Note 2)         $   .20        $   .17
                                    =======        =======


</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>

                                                            THREE MONTHS ENDED
                                                                  MARCH 31
                                                          1999              1998 
                                                       ---------         ---------
<S>                                                    <C>               <C>      
CASH FLOWS FROM OPERATING ACTIVITIES:

Net Income                                             $  33,173         $  27,986
Adjustments to reconcile net income to net
  cash provided by operating activities:
    Depreciation                                          25,937            25,937
    Decrease in receivable from General Partner           80,025            38,964
    Decrease in deposits                                      27                --
    Increase (decrease) in accounts payable and
      payable to limited partners                          3,300            (4,251)
                                                       ---------         ---------

      Net cash provided by operating activities          142,462            88,636

CASH FLOWS FROM FINANCING ACTIVITIES:

 Cash distributions to partners                          (77,718)          (67,908)
                                                       ---------         ---------

Net increase in cash                                      64,744            20,728

Beginning cash balance                                   101,404            75,411
                                                       ---------         ---------

Ending cash balance                                    $ 166,148         $  96,139
                                                       =========         =========

</TABLE>

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

                                      -5-
<PAGE>   6



                          DEL TACO INCOME PROPERTIES IV

                          NOTES TO FINANCIAL STATEMENTS

                                 MARCH 31, 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 March 31, 1999, the
results of operations and cash flows for the three month periods ended March 31,
1999 and 1998 have been included. Operating results for the three months ended
March 31, 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

                                 MARCH 31, 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 March 31, 1999, the two restaurants operated by Del
Taco, for which the partnership is the lessor, had combined, unaudited sales of
$409,568 and net income of $32,603 as compared to $387,499 and $19,216
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 March 31, 1999, the one restaurant operated by a Del Taco
franchisee, for which the partnership is the lessor, had unaudited sales of
$232,214 as compared with $216,069 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 March. The March rent was collected on April 10, 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 April 8, 1999, a distribution to the limited partners of $140,976 or
approximately $.85 per limited partnership unit, was approved. Such distribution
was paid April 24, 1999. The General Partner also received a distribution of
$1,424 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 MARCH 31
                                                    1999           1998
                                                 -------        -------

<S>                                              <C>            <C>    
Orangethorpe Ave., Placentia, CA                 $33,638        $31,675

Lakeshore Drive, Lake Elsinore, CA                27,866         25,928

Highland Ave., San Bernardino, CA                 15,510         14,825
                                                 -------        -------

                                    Total        $77,014        $72,428
                                                 =======        =======
</TABLE>

The partnership receives rental revenues equal to 12 percent of gross sales from
the restaurants. The partnership earned rental revenue of $77,014 during the
three month period ended March 31, 1999, which represents an increase of $4,586
from 1998. The increase in rental revenue was caused by an increase in sales 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:

<TABLE>
<CAPTION>

                            Percentage of Total
                      General & Administrative Expense
                      --------------------------------
                             Three Months Ended
                                  March 31
                             1999            1998 
                          -------         -------

<S>                      <C>             <C>   
Accounting fees             76.13%          75.09%
Distribution of
  information to
  limited partners          23.87           24.91
                          -------         -------

                           100.00%         100.00%
                          =======         =======
</TABLE>

General and administrative costs increased from 1998 to 1999 due to increased
costs for accounting and income tax return preparation.

Net income increased by $5,187 from 1998 to 1999 due to the increase in revenues
of $5,585 which was partially offset by the $398 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

(b) No reports on Form 8-K were filed during the three months ended March 31,
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:  April 30, 1999              /s/ Robert J. Terrano      
                                   ---------------------------
                                   Robert J. Terrano
                                   Executive Vice President,
                                   Chief Financial Officer


Date:  April 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>