Fast idle while driving?

Hi,

This vehicle has a throttle cable. Have you inspected it to make sure it isn't fraying or hanging up? The cable runs from the throttle pedal, through the firewall, and to the throttle body.

With the engine off, remove the air inlet tube between the air filter box and the throttle body. Have a helper gently press the accelerator pedal and gently release it. Check to see if the cable/throttle plate lever is returning fully to closed.

I attached two pics below. I indicated where you should lubricate the linkage. Try spraying a little penetrating fluid on that area and see if it changes what is happening. If it doesn't, then we will need to inspect the idle air control valve.

Let me know what you find.

Take care,

Joie

See pics below.

Thanks very much for your answer. I will take a look at it, though I'm not very 'engine savvy,' so might take it to a mechanic we have here. I've already had one look at it, but they were unable to solve the problem, so that's why I was writing to see if there might be something they haven't tried. I will let you know how it goes, but it might be a while till I can get to it. Thanks again for writing.

Actually, what I'm going to do first is look through my receipts and see if I can determine what was checked so far. I'll let you know what I find.

Hi,

Thanks for the update. Let me know what you find.

Take care,

Joe

I originally took the car in because it had a service engine soon light, and it was idling fast all the time (even when stopped in gear at an intersection). On that visit, they did the following:

Scan the vehicle for codes.
Clear codes: Lean 44
Check for vacuum leak, fuel pressure
Tighten side cover on transmission, adjust spring tension (had catch)
R&R Throttle position sensor, clean throttle body
R&R Mass air flow sensor
(+the usual oil change etc.)

When I got the car back, it seemed better. The service engine soon light was off and it idled slow when first starting and had a slow idle at stop lights, but something seemed off while driving and eventually I realized that the idle was bumping up fast as soon as the gas was applied with the car in gear. It made the car drive itself at about 30mph in 3rd and harder to stop. But once stopped the idle wound down to a slow idle, until the gas applied again. It doesn't happen in neutral (After starting one can step on the gas in neutral and it returns to a slow idle. It only happens in forward gear. I had read online that maybe unplugging the power to the computer and resetting might fix it so we tried that, but it didn't help.

I'm just wondering if you can think of anything else that might cause this. Did it sound like they did the lubrication you mentioned in your first post? Though would that problem affect the idle in both neutral and forward?

Thanks, John

They also replaced the oxygen sensor on that first visit.

Hi,

The idea that it changes only when in gear is odd. Do me a favor. Open the hood and have a helper start the engine and place it in drive so the engine increases. Check to see if the engine moves a lot when placed in gear. I'm wondering if a weak or faulty engine mount is causing the engine to move enough to affect the throttle. It's only a theory, but other than a possible PCM issue or wiring issue, it's the only thing that is making sense in my mind.

Have the helper apply the parking brake and hold his foot on the brake when testing. Also, to confirm there isn't a mounting issue, have them press the throttle in drive gently to see if that causes movement. Keep in mind, by nature, it will move. Excess movement indicates an issue.

Let me know.

Take care,

Joe

Thanks much for your thoughts. I'll try to check it in the next few days with a helper.

Hi,

You are very welcome. I know it may sound like a long shot, but anything is possible.

Take care and I look forward to hearing from you.

Joe

Hello again. I actually did more testing and the problem does happen in neutral. For example, if, as I'm driving and the car is idling fast, I put it in neutral, it continues idling fast until it rolls (or is braked)to a stop. Just after it stops, the idle will go down to a slow idle. But as soon as the car starts rolling again, the idle speeds up. It does it in gear and in neutral both.

Hi,

By chance, did the lean fuel mixture code return? Also, have you inspected the throttle body to make sure it isn't dirty and in need of service?

Take a look through this link and let me know if it helps in any way:

https://www.2carpros.com/articles/engine-idles-too-high

Let me know.

Joe

Thanks very much for all the suggestions here and in the link. I will bring this up with my mechanic and see what happens.

Hi,

You are very welcome. If you have a chance, let me know what is found. I'm interested in knowing.

Take care,

Joe