What are correct idle speeds for my 98 Bonneville?
Hot in park and in drive.
Cold in park and in drive.

JP

It should idle around 650 in park/hot, but when placed into drive, you will see a momentary drop in idle, but the PCM kicks it up the idle to prevent stalling.

What are you seeing?

Is it adjustable? Seems a little high maybe 900 in drive when warm. No vacuum leaks either.

The idle can be as high as 1500 RPM, depending on coolant temperature. Once the car is up to temperature, it'll be around 650. (Get Danthurs in here, he has a nice chart.)

If your idle is intermittently or constantly very high (say, 2000 RPM), check or replace your IAC valve.

Another question is what you are using to reference the engine speed. If it is the factory tach, you should be aware that they are not exactly known for their accuracy. Does it seem like it has a high idle?

It is adjustable with a tuner, but the factory settings are probably best and should not be lowered. I've got mine raised slightly.

If he changes his idle at the vehicles current state, in the future should he fix/replace whatever it was causing it to high idle, will now cause it to either not run at all, or be stumbling.

Find out what'* causing it first. As already mentioned, a vacuum leak or your IAC is causing this. Maybe IAT sensor also.

It sure runs great but idle does seem high. But the factory GM tach may just be off. History on this one, it had an intermittent stumble when accelerating when hot never when cold and ever single sensor has been replaced with no change what so ever. Nothinh ever showed up on the scanner. So I bought a pcm and got it installed and a new GM download.This is the best it has ever run or shifted. The stumble never came back. I never knew the correct idle speed hot when in drive or park. Was curious. Dan your comments please. It really does run super good and lots of power. Spun the tire and wasn't even trying.

JP