Intermittent fast idle - Toyota Nation Forum : Toyota Car and Truck Forums

murphy390 · 06-12-2009, 09:20 PM

This is on a 2000, 4 cyl, auto Camry. For a few months now the car will intermittently idle at 2000 rpms. This can last for 10 seconds or 20 minutes, the engine can be cold or warm, AC can be on or off, doesn't matter. It suddenly spikes and then eventually drops back down. My first thought, also after talking to a mechanic, was the IAC which I replaced. Also cleaned the throttle bosdy at that time. Problem still persists. Can't find any vacuum leaks either. A Toyota mechanic said it could also be the engine coolant sensor. So far no codes have been tripped to help me diagnose the problem. Anyone else seen this or have any suggestions?

Much thanks in advance!

Stillrunning · 06-14-2009, 09:04 AM

You can test the ECT sensor. I'd do it when engine hot and fast idle occurs. If bad ECT it usually also runs rich when hot and you get bad idle/rough running. Possible something is telling ECU to increase idle. If you bump gas pedal do rpms return to normal? Also look at accel cable. Idle-up on A/C is usually only about 500rpms so I doubt it's A/C related.

murphy390 · 06-14-2009, 10:30 AM

You're right, something is telling the ECU to increase the idle to 2000. My worst case scenario is that the ECU is going bad. The frequency of the fast idle has been increasing to the point where I experience it almost ever time I drive the car but it's not constantly at fast idle. Hitting the accelerator doesn't do anything. It doesn't run rich, there's no misfiring at the 2000 rpm's. I was able to have the hood open when it happened and shut down once and couldn't see anything around the throttle body moving. I'm going to swap out the ECT and see what happens. I was going to do the coolant anyways and at least the part was only $29. Thanks for your ideas.

***ASG14*** · 06-14-2009, 10:31 AM

Lets say, your stopped at a red light. Would it just jump to 2k RPM's while stopped, or would it stay at 2k RPM's when slowing down to the stop?

murphy390 · 06-14-2009, 11:14 AM

When it spikes it stays spiked until it "releases". If it has spiked and I'm coming to a red light I have to pay attention because the car wants to keep moving. The idle will drop to 1100 but that's only because it's in gear. If I slip it into neutral it goes back to 2000. Again, there's something telling the ECU to fast idle and then at some point the "signal" becomes normal and it will drop to the 600-800 range....only to spike again at some point.

Stillrunning · 06-14-2009, 04:42 PM

2000 rpm is about cold start fast idle, I doubt bad ECU as it relys on input signals to determine outputs. If you have low/no cost ECU to swap can't hurt. Check ECT sensor wiring for bare/short connection.

murphy390 · 06-14-2009, 08:47 PM

Swapped out the ECT and took it for a 15 minute test...all was well. My last name is Murphy and I wrote the law.....I'll wait till the end of this week before I declare victory and I'll keep the post updated for others.

murphy390 · 06-16-2009, 07:28 AM

Looks like the problem is solved and it was a bad ECT so if anyone has these symptoms that's the likely problem.

It's a very easy fix. I got the part at PepBoys for $29. You'll need to drain out some coolant from the radiator but not all of it, enough to get the level below the top hose going to the engine. The ECT is on the top of the engine right where the radiator hose connects. You'll need a 19MM deep socket to get it out. Remember to take the washer off of the old one and put it on the replacement. I put some teflon tape over the threads and then installed the new one. Top off the coolant and you're good to go!