High idle after driving

[S.hafsmo]

Yes, another idle topic.
My recent test drive revealed a few issues, and increased idle after driving is one of them.
When starting the car cold, it idles fine at approx. 7-800 RPM. At this point I can rev the car, even drive a little, but after it has reached operating temperature, it will not return to proper idle after driving or revving the engine. It's almost like it sticks to the coasting idle (1200 RPM) and won't return to normal.

It serves to mention that I've just been doing some work below the plenum, and I do not know if this was an issue before this work was carried out.
All gaskets are new, as well as all sub-plenum vacuum parts (hoses, grommets, actuators etc.), and I have eliminated most of these as the culprit by blocking of their vacuum supply. And regardless, would not a vacuum leak be unaffected by engine temperature?

I've also had the throttle body off, and while having it off, I checked if the DAG material was still there, which it was not. But again, would this be affected by temperature?

Found the primary throttle blade to be a bit small. This can't seal very well.


I've checked the IAC, and it does close properly.

[Roadster]

Seems like we have similar problems.....lol
Do you have a Tech 1 or scanner that will read the IAC counts? It would be interesting to see what your IAC is at idle. Hopefully we will both get our issues resolved......Good luck!!!

[S.hafsmo]

I actually ordered a tech-1 about 5 minutes ago. Will post the IAC-count as soon as I receive it.

I did some testing today with the car in the garage, but was unable to provoke the high idle. Seems it must be properly hot /driven for this to occur. Did however see a slight increase (900rpm) after revving a bit when engine was hot.

I did another test, which was inducing a vacuum leak by unplugging one of the plenum outputs (revs increase), disconnected IAC (IAC closes?), then reconnecting the previously removed vacuum connector. Should this not result in idle lower than normal? Stop screw set point? Idle did however seem to lower only down to 900 rpm, and stay there.

Engine stops if air horn covered with a plate.

[G8nightman]

I had a similar issue I had the TB off and placed a light under it to see that a good amount of light passing the blades this was also before i knew that it was bad to clean the TB and removed the dag by mistake. My fix was replacing the dag and idle went to normal after that.

[S.hafsmo]

Can one replace the dag?

[ssrszz4]

Force 842 moly lube can be used. It's a spray on.

Sent from my XT1585 using ZR-1 Net Registry mobile app

[Roadster]

Originally Posted by S.hafsmo

I actually ordered a tech-1 about 5 minutes ago. Will post the IAC-count as soon as I receive it.

I did some testing today with the car in the garage, but was unable to provoke the high idle. Seems it must be properly hot /driven for this to occur. Did however see a slight increase (900rpm) after revving a bit when engine was hot.

I did another test, which was inducing a vacuum leak by unplugging one of the plenum outputs (revs increase), disconnected IAC (IAC closes?), then reconnecting the previously removed vacuum connector. Should this not result in idle lower than normal? Stop screw set point? Idle did however seem to lower only down to 900 rpm, and stay there.

Engine stops if air horn covered with a plate.

From what I understand, if the engine stalls, then you are good with no vacuum leaks.

If you need to reset the IAC, this is from the FSM...
"Reset the IAC valve pintle position
A. Depress accelerator pedal slightly
B. Start and run engine for five seconds
C. Turn ignition "OFF" for ten seconds
D. Restart engine and check for proper idle operation"

Originally Posted by G8nightman

I had a similar issue I had the TB off and placed a light under it to see that a good amount of light passing the blades this was also before i knew that it was bad to clean the TB and removed the dag by mistake. My fix was replacing the dag and idle went to normal after that.

Now that I am thinking about it, it may have been possible when I had the plenum out I may have removed some of the dag on the primary throttle...


And yes, what did you use for the "dag"??? Was it the actual material, or something close to it???

[Roadster]

Originally Posted by ssrszz4

Force 842 moly lube can be used. It's a spray on.

Sent from my XT1585 using ZR-1 Net Registry mobile app

Sounds like I need to make a purchase.......

[ssrszz4]

Seems many throttle bodies use this factory applied dag stuff i did some research on may auto web site where they where having this same type of problem. Seems there's​the are a few different products that can be used but the force 842 seems to be the easiest to find they sell it on Amazon.

Sent from my XT1585 using ZR-1 Net Registry mobile app

[G8nightman]

It was a spray on i forgot the product I will take a picture and post when i get home.