Engine 1990 5.0 idle surge no error codes

redlxhatch1990 · Sep 16, 2018

Hello everyone,

I am new to thread and have tried everything on the surging idle checklist to solve my problem with no success. My car has edelbrock intake, 70 mm throttle body, 76 mm maf for 24lb inj. And 24 lb injectors.

My car was running great until it started surging and wanting to stall out of nowhere. The surging is very fast and erratic, unlike many slower surging cars I have seen in videos.

Car has new maf, IAC, distributor, injectors, vac lines, and TPS set within range. Fuel pressure is also good. This problem went away for me when i replaced the injectors but came back after a few days.

I have replaced vacuum lines that were old and that has not fixed my issue. I was wondering if anyone has an idea based on how it is idling what the issue could be.

View: https://youtu.be/xufXLrqz-5U

mikestang63 · Sep 16, 2018

do a search for the surging idle checklist

redlxhatch1990 · Sep 16, 2018

mikestang63 said:
do a search for the surging idle checklist

Thank you for your reply. I have gone through the checklist and it did not help in my situation. Do you know of any problems that will not throw codes but give a poor idle like mine?

mikestang63 · Sep 16, 2018

several. You went through that entire list and found nothing?
Did you disconnect the battery for 30 minutes to reset the EEC
Causes could be vacuum leak, IAC, TPS, bad grounds, 10 pin connectors, MAF, ECT, IAT, unmetered air getting into the motor, bad throttle body or intake gasket. idle not reset properly, timing off...

redlxhatch1990 · Sep 16, 2018

mikestang63 said:
several. You went through that entire list and found nothing?
Did you disconnect the battery for 30 minutes to reset the EEC
Causes could be vacuum leak, IAC, TPS, bad grounds, 10 pin connectors, MAF, ECT, IAT, unmetered air getting into the motor, bad throttle body or intake gasket. idle not reset properly, timing off...

Thank you for the tips, I have replaced and checked all vacuum lines, IAC, TPS, cleaned 10 pins, new MAF, ECT, IAT, checked gaskets. I will try to time the vehicle again and set the idle and TPS to see if that helps. I am just confused because the problem happened out of nowhere while driving, so I figured it'd be more of a sensor issue rather than a timing/idle issue.

jrichker · Sep 17, 2018

No code 11 (two flashes when the computer dumps the codes)? A perfectly functioning system will always get a code 11, it is the everything is OK code. The 11 code is computer passed its internal self test.
If you don't get an 11, you have computer or wiring problems.
Please check and repost.

redlxhatch1990 · Sep 17, 2018

jrichker said:
No code 11 (two flashes when the computer dumps the codes)? A perfectly functioning system will always get a code 11, it is the everything is OK code. The 11 code is computer passed its internal self test.
If you don't get an 11, you have computer or wiring problems.
Please check and repost.

No code 11 with KOER, I just get "cyl 8" which is not a cylinder balance code (which would be 80), but I believe it is identifying what engine I have through the computer. I will take a look at my computer and see if anything is fried. Never thought about that until you mentioned it!

redlxhatch1990 · Sep 17, 2018

and I just checked KOEO and get code 10 only

Mustang5L5 · Sep 17, 2018

Run the cylinder balance test.

That doesn't seem like idle surge to me. It almost seems like the engine just quits running and catches itself on a difference cylinder. Most IAC idle surge is typically a slower up and down surging. Try unplugging the iAC and see if anything changes.

Does it typical;ly idle that high, or when it was running right did it idle lower?

What heads are you running? 24#ers seem a tad bit for your combo.

redlxhatch1990 · Sep 17, 2018

I have the stock heads and cam. Needed new injectors and thought I'd be fine with 24's to support future mods as long as I have the correct MAF. After about a day of driving great the problem began.

Do you suggest using 19 lb. injectors and stock MAF to see if this fixes the issue?

It typically idles lower. Before it is warmed up it will miss (or whatever is happening) and once it is warmed up and the rpms drop then it almost stalls from the miss.

Steel1 · Sep 17, 2018

Why did you need new injectors, could it be that you replaced what you thought were faulty injector(s) but it's
actually a different issue?
That almost seems like it's periodically dropping a cylinder.

General karthief · Sep 17, 2018

Stick the 19's and the stock maf back on. From what I'm seeing and hearing I'd say you have a ignition cut off issue, like you are losing the fire at the distributor periodically. But thats an observation, go back to stock first, also reset the computer after the swap. Let us know what happens

redlxhatch1990 · Sep 17, 2018

I had this same issue last summer and a shop replaced the injectors and it solved it for the most part. It would still occasionally miss at idle or when I start giving it gas causing the car to jerk. I thought it was the injectors again but that did not fix it this time. I replaced the distributor last summer to rule out the pip sensor, but have not tried new plugs/wires yet.

I agree it is a miss and not a surge, I thought it was too quick to be a surge. Any suggestions on where to start? It has an MSD ignition system, and it really did suddenly die

General karthief · Sep 17, 2018

Was it doing it before the msd install?

redlxhatch1990 · Sep 17, 2018

Yes I have had the car for 3 years and it had the msd on when I got it. Randomly last summer this problem came up, went away for the most part, but now it's back. Very confused. I'll see how it runs with stock parts again and get back to you guys

redlxhatch1990 · Sep 19, 2018

stock injectors and MAF fixed the problem. Not sure why it was missing so bad before, the "calibrated" MAF is probably not enough and the vehicle would actually need a tune to run right, but tune won't be worth money until I have more bolt ons. Thanks everyone for the help!

General karthief · Sep 19, 2018

And another happy customer!
Glad you resolved the issue and posted the results.

Engine 1990 5.0 idle surge no error codes

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