high idle

A.Baker · Post by **A.Baker** » 22 Jan 2004, 08:59

My 87 740 jumps to a high idle for no reason, @ any time. Turbo boost gauge jumps as well but the turbo has been removed

HELP

Guest · Post by **Guest** » 30 Jan 2004, 20:09

how high is this high idle? i may be having the same problem with my '85 740 gle... sometimes it likes to idle at around 1,100 rpm, and when i put it in park or neutral, it revs to about 2,000 rpm. when i go to start the car later if i turn it off when it was idling high, it takes a lot of cranking to get it going again. I have suspicion of either the idler motor malfunctioning, but that normally causes the car to stall, or the throttle butterfly is not closing all the way, and causing the car to always have throttle applied.

Guest · Post by **Guest** » 30 Jan 2004, 20:11

figured i'd make a user for myself... the above post was me.

ozzimark · Post by **ozzimark** » 30 Jan 2004, 20:20

wow, that was funny... i hate doing three posts, but... yeah

A.Baker · Post by **A.Baker** » 30 Jan 2004, 22:18

Anonymous wrote:how high is this high idle? i may be having the same problem with my '85 740 gle... sometimes it likes to idle at around 1,100 rpm, and when i put it in park or neutral, it revs to about 2,000 rpm. when i go to start the car later if i turn it off when it was idling high, it takes a lot of cranking to get it going again. I have suspicion of either the idler motor malfunctioning, but that normally causes the car to stall, or the throttle butterfly is not closing all the way, and causing the car to always have throttle applied.

My idle concern is the same as yours.1,100 to 2,000. I called the local dealer for a $ amount on the idle control motor. It is 250.00 and they did'nt even blink. I decided to do some checking on my own and this is what I found. 1st. the motor is open during start up and continues to open with more rpm's you can see this with the motor in your hand and the pipeing blocked off.(a co2 cartridge works fine for this test.) 2nd. I started checking all electrical conections and found #7 and #15 pin out on the ECM rotted. I cleaned all conections and the problem has subsided some what. I get the high idle only after the engine is warm. but the no start has stopped. P.S. #7 pin is for the off idle switch on the intake plneum. I just bought a factory c/d on line and now I can fix the problem corectly. Chiltons is not a good sorce for electricel concerns.
I don't think our problem is mechanical I.E. throtle plate. fuel psi. and the like.
Keep in touch and when I fix mine I will post it for the world to see.

ozzimark · Post by **ozzimark** » 31 Jan 2004, 09:32

cleaning the connections helped some, huh? i'll have a look at it and i'll tell you if #7 and#15 are rotted on mine too. one thing that i've noticed works on my car to make it stop the high idle while i'm driving... if i notice that it's idling high, when i peg it, and make the trans drop a gear or two, the idle goes back to a normal speed. my guess would be that the sudden jerk to the engine knocks something into place, possibly the connection on #7, which would make sense, because you said that this was the high idle switch.

Volvord · Post by **Volvord** » 31 Jan 2004, 09:56

The IAC motors are known to "gum up" but can easily be cleaned by removing them and cleaning with a spray carb cleaner. Also check all your hoses for cracks and leaks.

Part of a regular tune up should include cleaning the IAC motor,and removing and cleaning the throttle body. Keeping these components in good condition improves the reliability and performance.

ozzimark · Post by **ozzimark** » 31 Jan 2004, 15:25

i'm assuming that by "IAC motor" you mean the idler motor... i'm not real handy with the real names of a lot of stuff. but if the motor gums up, wouldn't that cause a drop in idle, making it stall?

Volvord · Post by **Volvord** » 02 Feb 2004, 15:53

IAC is the idle air control motor, this is a stepper motor controled by the engine computer to maintain a constant ldle speed. When the motor gums up two things can happen, first the motor will not respond fast enough to the computers commands and a high or low idle will result. Second the air valve that is controled by the IAC may be gummed up and not allowing the valve to seat properly.

The fix is to clean the deposits from the motor and spindle area (air vale) so the IAC runs freely.

arete123 · Post by **arete123** » 03 Feb 2004, 07:10

Not to say this will work with yours, but I had high idle on my 81 240. So I cut the wire that went to the "smog" equipment and then adjusted the idle screw up to proper idle. It needs a little warm up now if cold to properly work but otherwise works good.