My '91 v6 is having a stalling/idle problem. It runs good when driving except when slowing down and stopped. It idles good in park and when in reverse with brakes on or rolling back.

Well, after several trys (listed below) it is still dying out in drive (brake on or offe) unless I turn up the idle screw. It idles well in park and in reverse with the brakes on.

I checked the codes and consistently get a 51 which points to the throttle position sensor. I tried checking the ohms at the connector per the manual but didn't really make a final conclusion. I wasn't sure if I had the feeler gauge correct at throttle stop screw and throttle - I mean the screw is adjustable so, couldn't that throw the whole think off?

Also, I got the "side mounted" idle speed control (ISC) valve off - cleaned it thoughly - and tried the electric test on it. Per the manual, I jumped the terminals with grounds and 12v and never saw the valve move open or close. If I did it right, it appears to be frozen open - it would touch terminals in sequence 1-2-3-4 for closed and the 4-3-2-1 for open positions. The reason I say open is because of all the carb cleaner that easily flushed through it while I was cleaning it. The Throttle body is oh so clean now too.

So, which is broke - throttle position (NAPA $100) or ISC (NAPA $510) or both? Or am I completely off track with just a shinney carb.[/align]

 

There should be no difference in idle for reverse or drive. The fact that reverse works fine and drive doen't leads me to ask what causes the idle to compensate for being in gear. Is it an electrical signal from the gear selector to the ECU or is it read from the TDC signal in the cam which sends the rpm signal to the ECU? It sounds like it's in the gear selector right now otherwise reverse would also cause stalling.

 

The solution turned out to be so simple, I'm almost embarrased. After cleaning the throttle body (and more), replacing the idle control valve (from salvage), testing the throttle position sensor (old and new), and other tests, I was ready to take it to the dealer.

A friend had a mechanic sayfor me to squeeze the air hose connecting the air filter housing to the throttle body while the car was idling. If the car cut off, check for a hose hole. !$%@@ that's what it was. There was a 3" slit on the bottom that I never saw taking the hose on and off. I always layed it down with the bottom face down. Squeezing the hose cut the car off just like putting it in park. I "seriously" wrapped the hose with electrical tape and it now runs like a champ - especially since the throttle body is clean enough to eat off of inside.

Lesson learned - keep checking the simple stuff until you know for sure it's something more complicated. Then check the simple stuff AGAIN !

 

So... check the hose to the IAC valve? Good advice mate.

 

i like it.,,