Surging idle and no start

Jfrost

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When starting, the idle surges 700-1200 rpms for a bit then will normalize, also happens when coming to a stop at times (car in neutral). I consider this pretty normal since I completed the engine swap into the Fiero and didn't think much of it till today.

I drove around about 30 min and then parked for an hour or so before starting again. It fired up and then died twice in a row, then the third time I gave it some gas and then it stayed running and the idle fluctuated again before normalizing. I can hear the fuel pump priming and running each time as it sits right below the center armrest so I don't feel it's a fuel issue.

First thought is it could be either the cam or crank sensor starting to go out. It's a junkyard engine with about 80k miles on it, so it could be time to replace them anyway. The engine is mated to a manual trans in my Fiero and has ran great until this mishap today.

I'm wanting to drive the car to central IL this Saturday and want to address this before it comes back again.
 

Jfrost

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Not sure why I didn't think of this first but could be the IAC valve, have a spare I could try out too.
 

Xfirez51

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Sounds like your crank and warm-up fuel tables need to be richer. Not sure what you're using but you could try flattening your timing and Fuel tables around the idle rpms.
 

ZephTheChef

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I had some issues like this with a car recently and just adjusted the throttle stop and it cleared right up. The TPS was reading 0% at idle. In my experience the computer likes to see a couple % at closed throttle. Not sure if it was the TPS being that low, or if that position was putting the idle at the limits of IAC adjustment or what, but it drives fine now.
 

Xfirez51

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I had some issues like this with a car recently and just adjusted the throttle stop and it cleared right up. The TPS was reading 0% at idle. In my experience the computer likes to see a couple % at closed throttle. Not sure if it was the TPS being that low, or if that position was putting the idle at the limits of IAC adjustment or what, but it drives fine now.
You bring up a good point and that is having the Min Air adjustment done properly. The TPS% will read 0, but you want to set the TPS volts to a certain range. On the GM stuff I have done, it's in the .52-.57v range for 0%.
 

ZephTheChef

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You bring up a good point and that is having the Min Air adjustment done properly. The TPS% will read 0, but you want to set the TPS volts to a certain range. On the GM stuff I have done, it's in the .52-.57v range for 0%.
I didn't play with it too much on the car I had the issue with recently to see what the actual voltage/reading was, but on the twincharged car, the trans would go into max line pressure mode if the TPS was reading 0% on the scanner at idle. I have it set at like 2% now and it's been fine. Of course, that's not apples to apples...we're talking about a Ford TPS and throttle body, no IAC, etc.
 

Xfirez51

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Code:
I didn't play with it too much on the car I had the issue with recently to see what the actual voltage/reading was, but on the twincharged car, the trans would go into max line pressure mode if the TPS was reading 0% on the scanner at idle. I have it set at like 2% now and it's been fine. Of course, that's not apples to apples...we're talking about a Ford TPS and throttle body, no IAC, etc.
Well w electronic throttle, GM has eliminated the IAC also.
 

Turbocharged400sbc

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on your note, check the paper tb gasket, they love to crack and vac leak

the other probability is the iac seat/passage has enough coking that its a "large" step in airflow at certain points, also if enough gets into the stepper shaft it'll gum up and stick in place momentarily
 

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