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]

Originally Posted by 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!!!

I've now received my Tech 1A and as expected, the IAC counts are 0 when the high idle occurs. I have not yet tested when it's cold.
When I parked today after a rather spirited drive, the idle was approx. 970 RPM, and after stop/start it stabilized at 770, so a 200 rpm drop by just restarting the car.

The Molykote D321R was stopped in transit, because it's "dangerous", so I've ordered it elsewhere. An expensive experiment at $120 for a bottle of spray.

Another issue has appeared, though probably unrelated. The battery voltage was 13.2 volts (on the Tech 1), which is way to low. Faulty voltage regulator? Increasing the revs did not seem to affect the voltage.

[Roadster]

Originally Posted by S.hafsmo

I've now received my Tech 1A and as expected, the IAC counts are 0 when the high idle occurs. I have not yet tested when it's cold.
When I parked today after a rather spirited drive, the idle was approx. 970 RPM, and after stop/start it stabilized at 770, so a 200 rpm drop by just restarting the car.

The Molykote D321R was stopped in transit, because it's "dangerous", so I've ordered it elsewhere. An expensive experiment at $120 for a bottle of spray.

Another issue has appeared, though probably unrelated. The battery voltage was 13.2 volts (on the Tech 1), which is way to low. Faulty voltage regulator? Increasing the revs did not seem to affect the voltage.

My idle issue exactly, only I don't have to do a spirited drive for it to occur. It will happen either driving normally or getting into it a little bit. Yes, restarts are exactly the same, will drop to normal after every restart...
As you may know I am in the middle of another plenum pull, so when everything gets backs together, hopefully the issue will be resolved.

I would check the voltage on your battery with the key in the off position, IIROC it shouldn't be below 12.5v (can't remember) and then check again with engine running as you already have. Another way to check besides the Tech 1 which should be accurate is to use a meter and put the pins directly on the "P" and "N" terminals to get your reading. But you may already know that.....
You can also put a trickle charge on it to see if the battery will take and is fully charged.

[S.hafsmo]

Originally Posted by Roadster

I would check the voltage on your battery with the key in the off position, IIROC it shouldn't be below 12.5v (can't remember) and then check again with engine running as you already have. Another way to check besides the Tech 1 which should be accurate is to use a meter and put the pins directly on the "P" and "N" terminals to get your reading. But you may already know that.....
You can also put a trickle charge on it to see if the battery will take and is fully charged.

I'm sure I checked the charge voltage just after I bought the car, but I obviously have to re-check. To completely fill an acid battery approx. 14.4V is necessary from the charger/alternator. The battery should then read 12,7V when the battery is fully charged.
Unless it has some sort of "float charge" that occurs when the battery is full. I'll try to double check later today.

[S.hafsmo]

Originally Posted by S.hafsmo

I'm sure I checked the charge voltage just after I bought the car, but I obviously have to re-check. To completely fill an acid battery approx. 14.4V is necessary from the charger/alternator. The battery should then read 12,7V when the battery is fully charged.
Unless it has some sort of "float charge" that occurs when the battery is full. I'll try to double check later today.

I re-checked the voltage the other day, and at least when cold it does make 14 Volts. Can I measure at the ALDL connector to check what the Tech 1 is reading?`

Originally Posted by XfireZ51

I'm pretty certain Marc would use the AYBK cal as the basis for any revised chip he would provide.

I would assume as much, the question was more in term of actually wanting the additions of the Mark chip. I can't seem to find any downside to it though.

[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?

[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???