Idle climbs to 1300 RPM only when car is stopped - Fine in netural car moving

[Peabody]

OK this is very interesting. I am the original owner of a 1990 240sx with 160,000 miles. I am having high idle problems so I cleaned the parts that I found on the forum and still have a high idle. I was going to replace the Idle control valve but I want to make sure it is that part before I spend $170 at Nissan.

I did not notice that if I am driving at any speed and put the car in netural with the clutch pushed in or with it out the RPM's stay around 550 and do not move. I have the idle screw turned almost all the way in so that is why it is low. Now when I bring the car to a stop the idle starts to slowly climb to 1100-1300 RPM's. This will happen with the clutch in or out.

So is there any speed sensor or something I can check to see why I get such a high idle only with the car not moving. I have turned the idle screw all the way in and that does not change anything. When I cleaned the ICV it did not have any dirt and looked great. I am not sure if the springs can wear out.

I was on a road with nobody around and I got to 85 and put it in nutural and coasted for minutes and the idle stayed at 550 RPM's. The second I came to a stop they started to climb back to 1200.

Has anybody had this problem or can someone tell me what I should look for or what to do.

THANKS

[vancouverbc]

If rpm stays around 550, you know your air regulator is not stuck open. I dont really know all the variables surrounding the idle. Your car may be heating up when you stop and the car has to work harder. Idle does bump up when the air conditioning is on. I might guess that your alternator is weak causing the high idle at stops. Sometimes it really isnt worth the effort posting the question because the answers really are not comprehensive enough to be useful. Most people only know what has happened to their car which makes for inadequate trouble-shooting.

[Peabody]

RPM's stay low only if I am moving with car in netural. Once I come to a stop they rise to 1250 RPM's. Not heating up at a stop, AC is not on, Alternator is fine.

I just thought it was odd that the idle jumps way up the second my car comes to a stop. If I could cost all day in netural it would stay at whatever I set it to (550-750). How can the stopping of a car make the idle just climb up so high. I posted this because I thought it might have happened to someone else.

Maybe I will just change the ICV and see what happens.

THANKS AGAIN

[guyaverage]

A misadjusted throttle position sensor can cause this problem.

[vancouverbc]

zerothread/161700

this article explains adjusting tps for 91-94 240's

[elpiar]

up from the dead.

I cannot find any other post that is as similar to my problem than this one. So, any takers?

[ELEMENT692121]

dose it do it only when your on the brake at a stop ?? ive seen a bad brake booster cause a similar problem before but it would only idle hi when you were on the brakes .. just for fun pull the hose of you brake booster and plug it off with somthing and see if it still dose it ..

[elpiar]

Does the ECU has a different idle setting when it's moving vs. when it's fully stopped?

[guyaverage]

Yes it does. The TPS, if adjusted too far advanced (in other words, telling the ECU the throttle is further opened than it really is) will produce a regular idle when rolling, but as soon as you stop the idle will creep up about 300-400 rpm higher. I've adjusted a billion of these, it happens like that every time.

Sounds like your TPS needs to be loosened and rotated up and towards the firewall.

(If your car is an automatic, it is not adjusted by voltage readings like 5-speed cars are. Check the manual, it tells exactly how to do it and if you dont do it that way, all sorts of goofiness will happen.)

[Peabody]

When I do turn it towards the firewall everything is fine but the voltage on the TPS is only .22 volts. The instructions for setting the TPS says the voltage should be between .44 & .54 volts. With setting mine at .22 volts to get the idle down does that mess up the air/fuel ratio or any other settings because it is not set to the correct voltage?

THANKS

[the converted]

Wow back from the dead. Get it between those ranges. Also are you using an auto ecu by chance?

[Peabody]

I did not mention that I have a air intake, header, no cat and I removed the IAA also. I am the original owner of the car and in 93 I changed out the ECU to a performance computer from Stilen. Back then you could not just install a chip. I can to buy their computer ($850) and then send my factory back to them for a core charge. With the new ECU it added about 12 hp and 15 lbs torque to the KA but I have to use premium gas. The bad part about this ECU is it has no lights and I cannot check any sensors. I have had no problems with this ECU for 14 years so I do not think it is my problem.

I just bought a new TPS and same thing if I set it to .44 volts the idle goes to 1500 with the car standing still. But if I set the voltage to .40 it will stay low and then climb after I take off and then stop the car but running in neutral it stays at 650 until I come to a stop and then after 30 to 40 seconds it goes to 1500 or even 1700 if I do not start moving again.

I also put in a new Jasper longblock in that now has 600 miles and it runs the same with the new motor as it did with my original block with 200,000 miles on it. All the hoses were chanced so I know I do not have a vac leak. I unplugged the egr valve and that did not help. Maybe it just wants the TPS to be set to .30 volts instead of .44-.55 for some odd reason.

I should have just done the SR-20 Swap but I live in New Orleans and could not find a shop.

T H A N K S

[Peabody]

I forgot to say when the TPS is set to .30 volts it will idle at 750 standing still but when I drive and take it out of gear the idle will be around 1500 RPM's until the car comes to a stop and then it will drop to 750 as I am slowing down. It is like the opposite of when it climbs when set to .45 volts. THANKS