93 5.0l E303 Idle Surge

[onefstssp]

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

 

[mikestang63]

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

@jrichker

 

[90lxwhite]

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

@jrichker

he's read it

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

 

[onefstssp]

Reading the help me create a idle surge checklist. Today messed with it best I can get it to idle is 850 with no surge until electric fan kicks on

 

[HrsPowr]

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...

 

[90lxwhite]

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...

The tps is non adjustable it works within a set range like you stated. You have to bore out the mounting holes in order to "adjust it. It's either in range or its bad. Fwiw when I did a cam in my 95 I ended up having to get a tune in order for it to idle but I've heard that the fox ecu's are more forgiving to mods than the 94/95's but I dunno.

 

[HrsPowr]

The TPS on the foxes has enough wiggle room to make quite a difference in the base voltage... I never had to elongate the hole, but you can get more adjustment that way. I do somewhat agree that it should be in range as mounted... And could just be bad or going bad.... Not a bad idea to clean all the connections with electrical contact cleaner too. It might have some corrosion and thus excessive resistance between the connectors. Most people just probe the wires and see good voltage but never check the connection itself. I've even taken the pins and sockets out of the plastic connector pieces and cleaned them with sandpaper to get a clean connection. Just be careful not to rub off the silver coating. I had this problem with an F150... I had an unsolvable misfire that drove me nuts until I disconnected everything cleaned all the connections and found one corroded pin at the ECU for a coil pack.