Cold Fast Idle Problem

[artbuc]

Re 99 RX300, initial engine rpm on cold fast idle is 2000 instead of 1500. RPM ramps down (more slowly than it used to, I think) as engine warms up and everything seems fine once engine reaches normal operating temperature. According to Toyota Technical bulletins, the ECM opens the IACV to a pre-programmed position based on coolant temperature and sensed rpm. (I don't understand what role the sensed rpm plays in the cold start idle program). As the engine warms up the rpm is gradually reduced until engine temp is 176 degs F. At that point the cold fast idle program ends and the ECM converts to a feedback idle speed control strategy. So, what would cause the initial cold start rpm to be 2000? The coolant sensor checks out perfectly and so does the IACV (that is, everything works according to the shop manual check-out procedure). I didn't check the rpm sensor, but don't understand how that could be a problem in this case.

Seems to me that the ECM is putting out the wrong signal to the IACV or the IACV is opening too much. I don't want to spend $200+ bucks for a new IACV if the problem is in the ECM. I don't get any engine error codes.

Is there a way to pinpoint the cause of the high initial cold start rpm? It is a pain driving a vehicle that wants to idle at 2000rpm.

[RX in NC]

What's your current mileage, and are you noticing increased oil consumption between oil & filter changes?

[artbuc]

What's your current mileage, and are you noticing increased oil consumption between oil & filter changes?

62k. Don't burn a drop. Change oil/filter every 3k or 3 months, which ever comes sooner.

[riwyle]

I would start by cleaning the IACV. This is easily done and may possibly be your problem. I always start with the easiest first. Do you have or do you know someone with experience doing minor auto maintenance?

I

[artbuc]

I would start by cleaning the IACV. This is easily done and may possibly be your problem. I always start with the easiest first. Do you have or do you know someone with experience doing minor auto maintenance?

I have already had the IACV off to inspect it. I didn't clean it because it looked pretty clean and was working freely. Coil resistances were in spec and valve opened/closed as it should when voltage was applied. I will take it off and give it a thorough cleaning unless someone else has a better suggestion.

[artbuc]

I appreciate the suggestion to clean the IACV but I was hoping someone could give me a more technical analysis based on the problem description. Am I asking the question wrong? Maybe I have a unique problem which has never happened to anyone else?

Oh well, I'll remove the IACV one more time and clean-it. If that doesn't work I'll buy a new one. Because my car is out of warranty, I don't want to take it to a dealer, especially since I am not getting any error codes.

[riwyle]

I appreciate the suggestion to clean the IACV but I was hoping someone could give me a more technical analysis based on the problem description. Am I asking the question wrong? Maybe I have a unique problem which has never happened to anyone else?

Oh well, I'll remove the IACV one more time and clean-it. If that doesn't work I'll buy a new one. Because my car is out of warranty, I don't want to take it to a dealer, especially since I am not getting any error codes.

Unfortunately I have seen no posts here by anyone with full expertise on the fuel and air computerized control systems on these cars. The best we can do is report back when we find a solution to at least increase our working knowledge to aid in future trouble shooting. Re. your problem- even though your symptoms do not match what has been posted in the past as being corrected by cleaning the idle air control valve, I would still clean it and the bypass port with a carburator cleaner, and see if it helps. Generally the symptems of a gummed up IACV are a failure to idle on start -up unless the accelerator pedal is slightly depressed and not a high idle speed as you are experiencing.

I found interesting in your previous post you stated that you had read that on start-up the IACV went to a fixed position and you did not know why an RPM signal was fed back. It was always my assuption that the idle speed set point was determined by temperature and other sensing devices, positiong the IACV, and the RPM signal was a feed back to verify the proper engine speed matches this set point.

I am also curious how fuel flow (injector pulse length) is determined at idle speed, since your high speed means you have too much fuel. Under normal running conditions I have assumed that the mass air flow sensor, possibly throttle position, and others, provide a feed forward signal to determine fuel flow, with O2 sensor trimming by a feedback signal. At idle speed, I would assume the MAF sensor is not sensitive enough to provide this signal.

These are the questions I would love to have answered to aid in my trouble shooting when and if required.