A couple of months ago I pulled and cleaned the plenum and idle air control valve housing, put in a new IAC valve and electrical connector, performed the min idle adjustment as detailed on the forum and now the car idles low when first started and is hard to keep running when started at op temp. Could the problem be the throttle position sensor? Thanks for any help and suggestions.

 

Could be. I suggest you redo the min air adjustment and check the TPS setting while there. A scan tool would tell you what the ECM is asking for. Also check for any "false air" sources.

 

My '86 is doing the same thing. So far I have replaced the IAC, the FPR and the fuel pump. So I'm thinking its probably the cold start injector. Thats next. I LOVE car COMPUTERS.

 

Thanks for the response guys. I guess I need to go to the min idle adjustment and begin again.
Jack, I understand from previous discussions on the board that the cold start valve only takes effect when the outside temp reaches a certain point. I think the statement was that above that temp. it was inactive. I didn't research it so I cant verify that fact so if you find out something different please post it.
Thanks again for the replies.

 

65ZO1 hit the nail on the head..you can spend a whole lot of time trying to figure your idle problem out. Re sycn your IAC and TPS...It couls something as simple as your VSS conector loose. Use, beg, or borrow a scan tool...it will show all

V/R,
Frank

86 1/2 vette Z-51 Lingenfelter 383 TPI
1985 ECM-165 (go figure)

 

Every now and then my '90 will do this.... it usually starts perfect and idles perfect, but sometimes it will start and not idle. It will seem like it's going to die. When I look at the IAC counts in Diacom, they are maxed at 160. I turn the car off and then restart it, and the IAC counts get back down to normal in the 40's and 50's at idle. What this is telling me is that the ECM is trying to open the IAC motor up, but for some reason it's not getting enough air to get the idle up. The ECM sees the IAC at max opening (160) and can't go any further. The idle meanwhile, is down at 400 or so and won't go up. Turning the car off and back on parks the IAC motor at the setting in the chip, which is around 100 on my car I think. Then restarting, the IAC gets back to the normal settings and the car idles again. The difference between my problem and whatever might be happening on yours is that I have an old IAC motor on my car and you have a new one. What I think is going on with my car is the IAC motor is dirty, and is not opening up all the way when the ECM tells it to. That's why I have low idle, but the ECM thinks the IAC is open all the way. Turning the car off parks the IAC motor, and maybe it loosens up in that process. Then when I restart, the IAC motor moves properly again, and idle is normal. It has only done this twice in the last month on my car, so it's not a big deal. Luckily I happened to have Diacom running the first time it happened. The only thing I can suggest is that you need to check for vacuum leaks..... reset the min idle again and maybe with the IAC motor unplugged, set the idle a little higher than the book says... I think it's supposed to be 450rpm with everything unplugged, set it to 500. Check that the IAC motor is not binding somehow. Hope you find out what it is, and let us know when you do!!