Surging idle and no start

Jfrost

TCG Elite Member
Dec 19, 2011
2,189
440
Brookfield
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.
 
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

Fast BoyZ of IllinoiZ
Jan 1, 2013
1,795
6
Northwest Chicagoland
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%.
 
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

Fast BoyZ of IllinoiZ
Jan 1, 2013
1,795
6
Northwest Chicagoland
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.
 
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