Idle question- interesting observation

[Dragowl]

So...as I'm getting acclimated with my vert, I notice that if I start the car and let her idle, the idle will start at around 1500rpms and slowly drop down below 1000rpms and maintain, BUT if I drive around and then stop and let the car idle, the car idles fairly high (1500rpms) and stays there...any reason why? I just find that a bit odd...

[jlevie]

A high idle on a cold engine that declines as the engine warms up is normal and expected. But once at normal temp the idle should be right at 750rpm. A high idle on a hotengine could be due to:

1) Bad or sticking ICV
2) Misadjusted throttle stop and/or TPS
3) Bad TPS
4) Intake leaks
5) Someone futzed with the idle bypass in the AFM

[Dragowl]

A high idle on a cold engine that declines as the engine warms up is normal and expected. But once at normal temp the idle should be right at 750rpm. A high idle on a hotengine could be due to:

1) Bad or sticking ICV
2) Misadjusted throttle stop and/or TPS
3) Bad TPS
4) Intake leaks
5) Someone futzed with the idle bypass in the AFM

Thank you much....I will look into the ICV, AFM and TPS....I've pretty much concluded that there are no intake leaks...I did change the AFM before thinking it was bad...but it may have been good, so I'll double check that.

[Dissembler]

Different engine-same problem. My 85 318 would start at 1800 and drop down to 1000 if i sat, and idled at 1200 if i drove away. turned out to be bad a icv. I replaced it and now it stays at just 750 period. try cleaning yours first, may save you some cash

[Dragowl]

Different engine-same problem. My 85 318 would start at 1800 and drop down to 1000 if i sat, and idled at 1200 if i drove away. turned out to be bad a icv. I replaced it and now it stays at just 750 period. try cleaning yours first, may save you some cash

Thanks...I'll check that.

[dkerley03]

M20 Rough Idle, Varies 500-750 RPM, Replaced TPS?

M20 Rough Idle, Varies 500-750 RPM, Replaced TPS and checked for vacuum leaks. The idle is still erratic, runs great at higher RPMs?

If we remove the oil cap the car dies! Is this normal, I know it draws vacuum through a large line on the valve cover?

My valves make noise, could poor valve adjustment cause my Idle problem?

[jlevie]

Are the TPS and throttle stop properly adjusted? The procedure is in the Bentley manual.

A sticky or bad ICV will cause the idle to hunt. Mis-adjusted valves can result in a low and rough idle.

If you remove the oil filler cap while the engine is running you introduce a large intake leak, which may cause the engine to die.

[pilotskillse30]

what if it holds at 750 rpm but idles rough, then it tries to compensate and holds 1000 still running rough with an intermitting hesitation. The rpms don't fish around it will stay at either one of those speeds.

[dkerley03]

Big improvement!

I removed and cleaned my idle control valve! It was nasty, but it made a big improvement in how my car idles! It increases RPM on start up and settles down and idles a lot better than it did! I still need to replace the sensor for cold idle that is in the thermostat housing, I tried ordering it from Peligan, but I chose the wrong part and accidently bought the on for the Temp guage readings? If anyone knows the correct Pelican part number I should order for my 1988 325IS, I would appreciate the input