93 5.0l E303 Idle Surge

mikestang63 said:

welcome. Try the search button as this question comes up several times a week. Look for jrichker's surging idle checklist.

@jrichker

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onefstssp said:

I'm new to the forum well sort of have been some threads on this site alot of good info on here. I have a 93 fox ssp car. Bought it from a friend. The engine was rebuilt by his work. It's a 306 stock bottom end, e 303 cam, gt40 heads they have been gone through bowl blended and gasket matched, gt40 upper and lower, stock throttle body, stock maf and injectors, factory airbox with k&n drop in, shorty headers and off road h pipe.


Things i have tried/replaced:
New distributor, new iac, new battery and cables

I have cleaned the throttle and maf. Had the idle to where it would only fluctuate a minimal amount but then at times it would just shut off as if you flipped the key along with it would slow crank did some research and a lot of people said pip could cause the issues. So I replaced the distributor now it surges a lot. Car has a performance qoutients balancer on it. Set timing and did base idle.. when i took the plug out ground strap was white to gray. Doesn't want to really idle steady at anything under 1k. And will sitting at lights car heats up rather quickly have a electric fan with thermostat have it set to kick on around 210. I'm thinking the car is lean if in a higher gear temp gauge will go up nothing crazy just small increments. Two things I'm going to do tomorrow check for any vac leaks and codes. Anyone have any suggestions or input about to pull my hair out have been reading surging idle checklist

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HrsPowr said:

You are on the right track with the vacuum leak testing. Spray starting fluid around all possible leak points and fix anything that you find. The throttle body has lots of possibilities. The IAC valve is rarely the problem but you should be sure its clean and not leaking at the gasket. Also what's the voltage at your TPS? I think it should be about .75 to 1 v... But its been a while since I've worked on a fox. You might call a company like Accufab and ask what the baseline setting should be. I think they will even check and set them if you send it in to John Mihovetz (spelling?). You can make small adjustments yourself by loosening the screws on the TPS. But you can also change the throttle blade with the set screw and mess everything up. Basically the blade should be virtually closed at idle and the IAC should be doing the work. Also make sure the MAF sensor is clean. If you have an aftermarket MAF then you must have it calibrated for the tube it is in. A company like Pro-M racing can help you with this. Lastly, the excessive heat does point to an air / fuel ratio problem that could be interrelated. Get yourself a wideband A/F meter and / or some dyno and tuning time to get that straightened out. Here's my surging idle checklist in order.
1. Check for and fix any vacuum leaks.
2. Clean IAC, MAF, and TB
3. Check voltages at TPS and possibly MAF
4. Adjust TB blade set screw and re-adjust TPS
5. Check and set base timing (TFI spout pulled) to about 10-14 degrees depending on elevation and fuel.
6. A/F ratio problem... Check / replace O2 sensors... Clean injectors... Change tune in ECU.
7. Internal issue.... Broken rings... Hole in piston... Bent valves... Etc...

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