Engine Idle Too Low

[lexus082]

When I first turn over the engine (cold) the rpms go up above 1,000 for a split second and then they come down to 750rpms and remain at 750 rpms until the engine begins to warm up. Then the rpms drop to about 400 then after a few more seconds they drop even lower down to 200 rpms. The car shakes when they get real low, but it doesn't stall out.

So far I have...completely cleaned the throttle body, cleaned the iacv, swapped mass air flow sensors and still have a low idle.

[SKperformance]

Turn your lights on/.

[lexus082]

I'm not sure I understand your reply, but when I turn on the headlights its doesn't help the low idle speed. When it starts to shake at a stop I turn the a/c on which seems to help a little.

[Lexls]

Try adjusting the TPS: http://www.lexls.com/tutorials/EFI/tps.html

[lexus082]

Tried adjusting the tps and turned it maybe a mm clockwise and then the idle speed went to 900 rpms. Then I turned it back slightly and it idle went back down to 500 rpms. I couldn't get anything in between that. It idled too low or too high. When it was idling at 900 rpms I turned on the a/c and the idle went down to 750 rpms. I had the same result when adjusting the tps on the other throttle body I had on the car just a few weeks ago. So I still have a low idle of around 500 rpms which then falls even lower after sitting at a traffic light. The engine hasn't stalled yet, but the car shakes due to the low idle speed.

[lexus082]

Could the ecu be receiving a untrue reading from a sensor causing this low idle speed. Nothing else was done to the car other than the starter being replaced. Not sure if its related to that or not. Maybe a sensor that is going bad but not bad enough yet to trigger the check engine light? My tach needle goes all the way down to the first mark on the tach which I think is 250 rpms. Thats what it idles at when warm and in park. Could this be related to the fuel system? Or could worn or old plugs, rotors & caps cause a low idle speed? I've cleaned the throttle body, swapped MAF sensors, adjusted tps, cleaned IACV. Still no luck.

[ko90ls]

My 90 LS has been doing this for a few years now. When cold outside Idle is 700/750 until car engine is of correct temp then idle slowly drops to 200 rpm. when driving car cruises at 750 rpm but when at a stop idle srops to 200 rpm(250 if a/c is on). after reading much on this issue I think the problem is due to a vacuum leak. a hose on my air intake is broken as well as the BVSV valves (yes both) Check the BVSV valve as my idle was low before the air intake hose broke. If you look on the drivers side of the engine you should see a small hose connecting over the LH timing belt cover, this connects to the BVSV valve.

[lexus082]

Have you fixed your problem by replacing this valve? Not sure what little hose you are referring to. Is there just one bvsv valve to inspect? Where does the BVSV valve mount to the engine? Thanks

[theoldpaths]

What is the correct idle speed when cold and when fully "warmed up". Mine idles at about 1700 when first started cold, and that seems high. It really "clunks" into drive when idling at that speed and I don't always have time to sit and wait for it to warm up.

[pishta]

What is the correct idle speed when cold and when fully "warmed up". Mine idles at about 1700 when first started cold, and that seems high. It really "clunks" into drive when idling at that speed and I don't always have time to sit and wait for it to warm up.

I think the correct idle is about 650 +- 50 at idle in or out of gear w/AC off. AC may raise your idle to about 750 but it usually stabalizes. Lights may alter the idle a minute amount. The idle is set by the ECU so I dont think the TPS would affect the true idle circuit. The IAC just meters a small amount of air around the closed throttle plate and the injectors get a short duty cycle from the ECU. I dont know of any "hardware" fix to raise or lower the programmed idle. I would seriously consider a vacuum leak. A vacuum leak will cause the idle to be very lean as the iac would get a signel from the ECU to close becasue it already sees air in the intake, kinda complicated, but a vacuum leak in a carbureted motor causes a high idle that is very lean and has absolutely no power. You can look at the vacuum hose diagram on the hood and start pinching soft lines with a plier to see if you can isolate the leak. Do it while idling to see if any pinched lines casue the idle to raise. That or a bad coil, does the exhaust smell of strong unburned gas? Bummer....You can also try and reset the ECU, just pull the negative cable for about 30 minutes.

[theoldpaths]

What is the correct idle speed when cold and when fully "warmed up". Mine idles at about 1700 when first started cold, and that seems high. It really "clunks" into drive when idling at that speed and I don't always have time to sit and wait for it to warm up.

I think the correct idle is about 650 +- 50 at idle in or out of gear w/AC off. AC may raise your idle to about 750 but it usually stabalizes. Lights may alter the idle a minute amount. The idle is set by the ECU so I dont think the TPS would affect the true idle circuit. The IAC just meters a small amount of air around the closed throttle plate and the injectors get a short duty cycle from the ECU. I dont know of any "hardware" fix to raise or lower the programmed idle. I would seriously consider a vacuum leak. A vacuum leak will cause the idle to be very lean as the iac would get a signel from the ECU to close becasue it already sees air in the intake, kinda complicated, but a vacuum leak in a carbureted motor causes a high idle that is very lean and has absolutely no power. You can look at the vacuum hose diagram on the hood and start pinching soft lines with a plier to see if you can isolate the leak. Do it while idling to see if any pinched lines casue the idle to raise. That or a bad coil, does the exhaust smell of strong unburned gas? Bummer....You can also try and reset the ECU, just pull the negative cable for about 30 minutes.

So it should be about 650rpm cold? Mine is about that when warm, but seems very high before warming up.

[pishta]

What is the correct idle speed when cold and when fully "warmed up". Mine idles at about 1700 when first started cold, and that seems high. It really "clunks" into drive when idling at that speed and I don't always have time to sit and wait for it to warm up.

I think the correct idle is about 650 +- 50 at idle in or out of gear w/AC off. AC may raise your idle to about 750 but it usually stabalizes. Lights may alter the idle a minute amount. The idle is set by the ECU so I dont think the TPS would affect the true idle circuit. The IAC just meters a small amount of air around the closed throttle plate and the injectors get a short duty cycle from the ECU. I dont know of any "hardware" fix to raise or lower the programmed idle. I would seriously consider a vacuum leak. A vacuum leak will cause the idle to be very lean as the iac would get a signel from the ECU to close becasue it already sees air in the intake, kinda complicated, but a vacuum leak in a carbureted motor causes a high idle that is very lean and has absolutely no power. You can look at the vacuum hose diagram on the hood and start pinching soft lines with a plier to see if you can isolate the leak. Do it while idling to see if any pinched lines casue the idle to raise. That or a bad coil, does the exhaust smell of strong unburned gas? Bummer....You can also try and reset the ECU, just pull the negative cable for about 30 minutes.

So it should be about 650rpm cold? Mine is about that when warm, but seems very high before warming up.

Its high but goes down to 650 after about 30 seconds. I think it is high to warm the cats and get them operational. The BMW uses an electric heater to get theirs cooking! Wow, just thought of something...wonder if the cats or 02 sensors have anything to do with this problem??? like do they put the ECU into a closed loop mode until they get heated and that is casuing the idle to be off? Any FI gurus in here that can theorize this condition?

[SKperformance]

All cars do not take o2 sensors readings until they reach a certain temp as they will not make usable readings until hot.

[wonknose]

So it should be about 650rpm cold? Mine is about that when warm, but seems very high before warming up.

On mine the idle is pretty fast when cold and causes the car to really pull when put in reverse-- was following this link to see if anyone else knows how to bring the "cold" idle down.