won't idle
 

89 na manual. will not idle. I've replaced the tps, and it fixed the high idle problem I was having, tried putting the old one back and didn't change anything. I can keep it running by raising the rpm, but on its own it just drops and dies. out of gear it idles rough while I hold it, but in gear it goes through the whole rpm band with no problems... fuses all fine, can't check the timing cause it won't idle, but it just passed emissions, and I don't think the timing belt jumped cause it runs just fine off idle

ok, just tested the tps and iac(isc) all checked out fine, the car does seem to try to idle with the iac unplugged, it will stumble once or twice, with it plugged in, it just drops instantly after you let off the gas.

checked the codes, I've got 41 (haven't cleared after replacing tps) and 24 which I believe is something to do with the knock sensor? would this not let the car idle?

Code 41 is a fault in the throttle position sensor signal.
Possible trouble points:

• Throttle position sensor
• Throttle position sensor circuit
• ECU

Code 24 is a fault in the intake air temperature sensor.
Possible trouble points:

• Intake air temperature sensor circuit
• Intake air temperature sensor
• ECU

tested everything in the afm, all in spec

ok, got some alligator clips and tested the operation of the isc. unless it is supposed to move a lot, I think it is frozen. when I ground the s terminals, the valve twitches but doesn't actually move...

ISC operation
 

I realize it has been a year since your post, but thought I would tell you what I know about the Idle Speed Control Valve. I am trying to solve a loping idle problem and when checking the ISC, I thought it wasn't moving until I realized that you must repeat the sequence S1-S2-S3-S4---S1-S2-S3-S4 over and over. With each sequence it will move slightly out. When you reverse the sequence S4-S3-S2-S1 (over and over) it will move back in.

By the way, anyone have a clue on intermittent loping idle around 500-600 rpm? Not getting any codes and ISC checks OK. TPS also checks out ok per TSRM. I have looked for vacuum leaks, but no luck except there is a hissing sound around the EGR vacuum regulator that I cannot pinpoint. I will check the EGR vacc reg per the TSRM (EC-13).