'91 V6 Idle/stall when shifting to drive

[just2day]

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.

When it started doing this, I replace a leading front valve cover gasket due to oil in the plut tubes, put in new plugs, but no impact. I check on the forums and then cleaned the throttle body really good which helped the idle when parked and in reverse, but now it still dies when coming to a stop in drive or just sitting there with the brakes on in drive. I looked over the vacumn hoses - found one small crack and fixed it - no help.

Before changing the cover gasket and plugs, I thought my wife had gotten some bad gas and treated for that too. I put in high octane (93 exxon) and some STP treatment - but no difference yet. Also, several weeks ago I replaced the MAF and after that it ran like a top for several weeks. Then this just started. I've checked the connections to everything but haven't found anything loose (yet).

I just find it strange that it idles in park fine AND in reverse with brakes on but dies in drive unless I give it gas. Also, when I start to go in drive, it is very sluggish until building up some speed (20mph) and then seems OK. It starts up immediately after stalling off.

Has anyone heard of this situation? I don't have a computer code tool and hate to take it to a dealer just to put on the diagnostic or, worse, have them do a costly but simple repair that I could have done.

[Mike Gerber]

just2day,

See my answer in the other thread where you posted this question.

Mike

[cactus88]

My 88 3sfe has the same problem, I think that it is the engine mounts, I can idle in neutral with the hood up and when I put it in drive the engine rocks back and then dies, It will start up easily and if I give it gas the engine jumps around. When I put the shifter in reverse the engine tilts to the front of the car very little and idles fine. let me know if this helps.

[Mike Gerber]

"My 88 3sfe has the same problem, I think that it is the engine mounts"

Worn engine mounts can cause a vibration, but they will not cause the car to die.

Mike

[just2day]

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.

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.