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Poor Idle with Holley 502-3

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  • #1

    Poor Idle with Holley 502-3

    The Holley 502-3 is the replacement TBI for 2.8L engines, having 400cfm. I had it on my 2.8 for a long time. My original had a worn throttle shaft so I opted for the Holley. It never idled well but well enough, rich.
    Then I built my 3.1 and used the same Holley TBI and bored the manifold out to the size of the gasket, a 4.3 gasket was the same size as the Holley throttle bore. It idled OK but again, not great.
    So recently I put a set of Comp Cams 1.52 roller tip rockers on the 3.1. It now idles very badly. Part throttle has a surge. Pedal to the floor performance is excellent, no misses and it pulls strong. In my signature you can see my particulars.
    I cleared the ECM memory and reset the IAC. Small improvement, but very small. Are the rockers causing it to run richer (more lift) or are the rockers out of adjustment? I have read that the Holley will run rich no matter what you do but I had no major troubles with it until I changed the rockers. I haven't readjusted the TPS yet but it, as the IAC were undisturbed.
    Timing is right on. The rockers are adjusted "0" plus 3/4 turn.
    I'm thinking of going back to a stock TBI to see if this helps. Should I go over my valve adjustment again? Could this be the problem?

    Thanks
    '86 S10 Blazer 4WD, '87 2.8 with 3.1 crank and pistons, A.R.I. "Stage 2 Cam", Iron Heads with stiffer springs, Holley TBI, Manifold bored to fit the TBI Base(4.3 size), Fiero Covers, MSD Coil, DynoMax Muffler and 2.5 Tailpipe, no cat, Auburn Limited Slip, 3.73 final Drive. 700R. '85 Fiero GT 3.4 Hybrid, relieved top intake and exhaust, 57mm TB, Auto. 3.06 final drive.
    Tags: None
  • #2
    MAP sensor plug pulled out part way do to fighting the Fiero covers on and off.
    '86 S10 Blazer 4WD, '87 2.8 with 3.1 crank and pistons, A.R.I. "Stage 2 Cam", Iron Heads with stiffer springs, Holley TBI, Manifold bored to fit the TBI Base(4.3 size), Fiero Covers, MSD Coil, DynoMax Muffler and 2.5 Tailpipe, no cat, Auburn Limited Slip, 3.73 final Drive. 700R. '85 Fiero GT 3.4 Hybrid, relieved top intake and exhaust, 57mm TB, Auto. 3.06 final drive.

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    • #3
      Glad to hear it was a simple fix!
      -Brad-
      89 Mustang : Future 60V6 Power
      sigpic
      Follow the build -> http://www.3x00swap.com/index.php?page=mustang-blog

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      • #4
        Wrong again, I am. Idled OK for awhile then back to loping and erratic idle. I'm afraid it's a valve issue. Covers off tomorrow. When I first put the rockers on I had a push rod slip out of the rocker and jam up, holding the valve open. Bent the push rod and it was very difficult to get out. Only ran for 20 seconds before I shut it down. I am thinking that if nothing is damaged putting the stock rockers back on and getting rid of the Comp Cams stuff, they haven't worked well from the beginning. I think the "leave well enough alone" theory may be the answer for me.
        '86 S10 Blazer 4WD, '87 2.8 with 3.1 crank and pistons, A.R.I. "Stage 2 Cam", Iron Heads with stiffer springs, Holley TBI, Manifold bored to fit the TBI Base(4.3 size), Fiero Covers, MSD Coil, DynoMax Muffler and 2.5 Tailpipe, no cat, Auburn Limited Slip, 3.73 final Drive. 700R. '85 Fiero GT 3.4 Hybrid, relieved top intake and exhaust, 57mm TB, Auto. 3.06 final drive.

        Comment

        • #5
          Took the covers off today and readjusted the valves, a little loose. Still didn't help the idle. I can't find a vacuum leak with carb cleaner. Wits end. It ran fine until I changed those damn rockers. What does an ECM do when mods are too much? I've got another ECM, I wonder if that's the fault? I've set and reset the IAC so many times it's ridiculous.
          '86 S10 Blazer 4WD, '87 2.8 with 3.1 crank and pistons, A.R.I. "Stage 2 Cam", Iron Heads with stiffer springs, Holley TBI, Manifold bored to fit the TBI Base(4.3 size), Fiero Covers, MSD Coil, DynoMax Muffler and 2.5 Tailpipe, no cat, Auburn Limited Slip, 3.73 final Drive. 700R. '85 Fiero GT 3.4 Hybrid, relieved top intake and exhaust, 57mm TB, Auto. 3.06 final drive.

          Comment

          • #6
            You mods are not over the top. Unless that stage 2 cam is a crazy grind. What are the specs?

            The first thing I would do is check the fuel pressure. You may need to adjust it. The Holley is adjustable from the factory.

            The rockers you installed are such a tiny change they would not make a difference.
            1993 EXT. CAB, 3.4L V6 TBI, 5spd manual. Sonoma
            1990 4Door, 3.2L V6 TBI, 5spd manual. 4X4. Trooper
            Because... I am, CANADIAN

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            • #7
              I don't know about the roller tips, but my stock require 1 1/2 turns after contact.
              1994 Isuzu P/U - 3.1L Iron Heads many mods

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              • #8
                I just e-mailed Holley about the fuel pressure. Is under the little soldered on plate?
                cam specs 204-214 @.050, Adv. 270-280, lift .420, .443, lobe centers, 107, 117.

                It all went to hell after the addition of the Comp Cams 1.52 rockers. I've adjusted them twice. I've replaced the map, the temp sensor(not the one for the gauge, Checked for vacuum leaks, new plugs, adjusted and replaced the IAC, readjusted the TPS.
                I read that the '89 ECM is better to use for performance than the '86 1227429, '89 1220062. I haven't tried that yet. I'll try the fuel pressure adjustment first. I've read that you can't lean it out too much.

                I've left alot out but thanks for all the replies, if you think of a magic bullet, please tell me.
                Last edited by Ray Hamilton; 05-22-2008, 03:14 PM.
                '86 S10 Blazer 4WD, '87 2.8 with 3.1 crank and pistons, A.R.I. "Stage 2 Cam", Iron Heads with stiffer springs, Holley TBI, Manifold bored to fit the TBI Base(4.3 size), Fiero Covers, MSD Coil, DynoMax Muffler and 2.5 Tailpipe, no cat, Auburn Limited Slip, 3.73 final Drive. 700R. '85 Fiero GT 3.4 Hybrid, relieved top intake and exhaust, 57mm TB, Auto. 3.06 final drive.

                Comment

                • #9
                  What does your TPS read at idle?
                  1993 EXT. CAB, 3.4L V6 TBI, 5spd manual. Sonoma
                  1990 4Door, 3.2L V6 TBI, 5spd manual. 4X4. Trooper
                  Because... I am, CANADIAN

                  Comment

                  • #10
                    Holley says to set it at .65 but I have it at .59. I changed the ECM today, apparently the one I put in was for a standard trans cause it wouldn't shift into OD. Put the old one back in. Reset the ECM again and the TPS again. Runs like shit. Tomorrow, off with the Comp Cams Rockers and back to stock. I don't know how it could be responsible for this but that's when the shit hit the fan. When I first put them on I had a push rod slip out of one and back fire, only ran for about 15 seconds. I took the rocker off and like to never got the push rod out. It was bent so I put in another new one. As far as rockers go everything seemed OK except this poor idle and mid throttle situation. When I first built this engine last summer, when I got it in it started up and ran like a champ and has been running that way since, until...............
                    If it was a carburetor I would say the power valve blew out when it backfired, that's common for Holleys, then the gas POURS into them.
                    When I readjusted them the first time they had loosed up, so I reset them again with only 1/4 turn after the push rod was tight. I might add that I adjusted the valves stone cold static. If they need to be adjusted pumped up, can you spin over the engine with the starter until pressure is achieved and adjust that way? The Fiero covers are a bitch to get off cold much less hot.
                    Last edited by Ray Hamilton; 05-23-2008, 12:05 AM.
                    '86 S10 Blazer 4WD, '87 2.8 with 3.1 crank and pistons, A.R.I. "Stage 2 Cam", Iron Heads with stiffer springs, Holley TBI, Manifold bored to fit the TBI Base(4.3 size), Fiero Covers, MSD Coil, DynoMax Muffler and 2.5 Tailpipe, no cat, Auburn Limited Slip, 3.73 final Drive. 700R. '85 Fiero GT 3.4 Hybrid, relieved top intake and exhaust, 57mm TB, Auto. 3.06 final drive.

                    Comment

                    • #11
                      Oil in the lifters makes no difference as far as adjustment goes. Also if you had a backfire at one point you may have destroyed the MAP sensor that is very common. Having a pushrod pop out is odd. Sounds like you did not add enough preload. If you are using stock studs you need AT LEAST 1 turn of preload. If they are after market studs then 3/4" is enough.
                      1993 EXT. CAB, 3.4L V6 TBI, 5spd manual. Sonoma
                      1990 4Door, 3.2L V6 TBI, 5spd manual. 4X4. Trooper
                      Because... I am, CANADIAN

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                      • #12
                        I did an running valve adjustment. What a mess. 4 qt all over my yard,. I haven't driven it but it sounds alot better.
                        For anyone doing a running adjustment, add oil half way through! This is the way I always adjusted my old chevy V8's, 265's, yes I said 265's, and 283's. Had a 55 Nomad, 2 '56's, 2 dr hardtop, 2 door post, '57 2 door post, '41 coupe with a 301 in it, 11 to 1 FI pistons. Before I was 19. All gone when I got drafted. Thanks uncle sam.
                        '86 S10 Blazer 4WD, '87 2.8 with 3.1 crank and pistons, A.R.I. "Stage 2 Cam", Iron Heads with stiffer springs, Holley TBI, Manifold bored to fit the TBI Base(4.3 size), Fiero Covers, MSD Coil, DynoMax Muffler and 2.5 Tailpipe, no cat, Auburn Limited Slip, 3.73 final Drive. 700R. '85 Fiero GT 3.4 Hybrid, relieved top intake and exhaust, 57mm TB, Auto. 3.06 final drive.

                        Comment

                        • #13
                          Well thats one way of doing it. I prefer not making a mess and I just do 1 valve at a time.
                          1993 EXT. CAB, 3.4L V6 TBI, 5spd manual. Sonoma
                          1990 4Door, 3.2L V6 TBI, 5spd manual. 4X4. Trooper
                          Because... I am, CANADIAN

                          Comment

                          • #14
                            Made a mess all right and didn't make any difference. I took them off yesterday and they are for sale here at the store. I'll give the folks here a chance at them before I put them on e-bay. Thanks for your replies.
                            '86 S10 Blazer 4WD, '87 2.8 with 3.1 crank and pistons, A.R.I. "Stage 2 Cam", Iron Heads with stiffer springs, Holley TBI, Manifold bored to fit the TBI Base(4.3 size), Fiero Covers, MSD Coil, DynoMax Muffler and 2.5 Tailpipe, no cat, Auburn Limited Slip, 3.73 final Drive. 700R. '85 Fiero GT 3.4 Hybrid, relieved top intake and exhaust, 57mm TB, Auto. 3.06 final drive.

                            Comment

                            • #15
                              Well I feel you are giving up way too easily. Since the difference between 1.52 rockers and the stockers it minute. Also consider the fact that factory rockers are sot very precise so you probably have some 1.52's and some 1.48's. It is really not a big factor. My guess is you still need to fully understand valve adjustment and do it correctly and then go ahead and diagnose the motor and find the real cause of the problem. Did you ever do a compression check with the stock or the Comp rockers?
                              1993 EXT. CAB, 3.4L V6 TBI, 5spd manual. Sonoma
                              1990 4Door, 3.2L V6 TBI, 5spd manual. 4X4. Trooper
                              Because... I am, CANADIAN

                              Comment

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