wierd idle and stall issue

[JasonBVHS]

For some odd reason, if I come to a sudden stop, and I mean a real sudden stop, the engine almost stalls out. the tach goes down to around 500 surges up to 1500rpms only once and all is well. the second issue I have is a slight shudder in the front when idling, but it doesn't register on the tach, but you can feel it, and if you look in the engine bay it's very slight, but visible. I've replaced all of the coil packs with new ones, new spark plugs, new alternator, battery, cleaned the MAF, new IAT, replaced all the intake gaskets,, all new O2 sensors. the only thing i can think is to have a bad injector, but i'm not sure how to prove this, nor if that would be the culprit, because as I said its real slight, and it definitely isn't a misfire. Oh and the cams are welded.

 

[Vnuk1]

Not throwing any codes?

 

[frosho]

ATX or MTX? Did you replace the plug wires when you did the plugs?

 

[SHOMON]

ATX or MTX? Did you replace the plug wires when you did the plugs?

There are no wires.

 

[JasonBVHS]

there are no CEL or pending codes at all, and it's an ATX.

 

[frosho]

There are no wires.

Dur! I should've known when he said coil packs.

How about the IAC? Did you replace or clean that?

 

[JasonBVHS]

yes that has been replaced

 

[Izzmo]

I think this is a pretty common issue. Paul has fixed a few people's with the help of a tune on this.

 

[Brydakidz]

It's happend to me a few times too. Usually happens to me when I have everything electronic on, but that not always the case. Never been able to pinpoint the problem though.

 

[SHOZ123]

What I do is to adjust the throttle stop screw. Cured mine of stalling occasionally.

With a warm engine screw the stop in until the motor is running around 1500 rpm. Then disconnect the IAC. Then screw the stop out so the car idles around 400 rpm. Then shut car off, plug IAC in and disconnect the battery. Restart and let the car relearn the idle.

In the end you should be about a 1/4 turn in past contact with the throttle stop.

 

[JasonBVHS]

I adjusted the throttle stop screw, but whenever i screwed it out to achieve any idling rpm under 900, this is with the motor warm, the accelerator sticks. on top of that I can not achieve a normal idle of 750 under any circumstance. The throttle body is cleaned, I cleaned the entire upper/lower intake manifold as well as the tb when I did the motor and tranny sway. Plus why would my motor idle consistently between 900-1000?

 

[SHOZ123]

If the IAC is good then the high idle may be the TPS, see if it is under .99V when the throttle is closed. Or a vacuum leak.