that's right, another high idle thread.

[long tall eta]

HELP, last week my idle became very eratic jumping from 800 down to 500 and back on a rhythmic patern. gave her the once over and found a cracked elbow boot. replaced that today and now i'm up around 1300 with speratic drops to 800. it does not surge with the heater blower on 3 and 4 settings. i don't know what that could have to do with it. these idle readings are taken with the icv screw turned all the way in. if i back it out, the idle will increase even more. did the carb cleaner leak hunt and found nothing. no access to smoke tester for a few weeks. all hoses that are visable are secure and in good looking condition. i tried 2 other known working icv's with no luck. grrrr

[long tall eta]

before i had the high idle, if i pulled the dip stick the idle would drop. same thing with the oil filler cap. if i remove the icv hose from the intake boot, same thing, she drops. the cracked boot resulted in a reduced idle. what lines/hoses should i be looking for that would make her idle high if they where bad??

[dnguyen1963]

If you don't have access to a smoker then do the cigar method to find the gross vacuum leaks. There are many places that could be the cause, brake booster hoses, throttle body elbows, valve cover gasket, to name a few.

[long tall eta]

UPDATE: problem seems to be coolant temperature related. when first started this morning, car idled at 900 where she always has when cold. once cold start injecter cut off she dropped to a perfect 750. only once the coolant temp started to rise did the idle climb. which of the t-stat housing sensors would cause this?

[long tall eta]

If you don't have access to a smoker then do the cigar method to find the gross vacuum leaks. There are many places that could be the cause, brake booster hoses, throttle body elbows, valve cover gasket, to name a few.

i agree, but all the previous vac leeks I've had produced low or stumbling idles. this is a steady high idle only present when the coolant temp rises.

[long tall eta]

which, if any, of the sensors in the t-stat housing would cause my eta to idle high?

[long tall eta]

ttt

[95BMWIC]

When the engine is cold, the fuel system supplies the engine with additional fuel, when it warms up the fuel is slowly reduced. Engine temperature info is sent by the coolant temp sensor and or (depending on year and model) the coolant temp switch.

Identify your Model:

L-Jetronic models received
Coolant temperature switch/sender (12621285073) The switch is an input for both the vacuum advance control relay and the idle control unit. The sender side is for the gauge. It's a 2 pin hookup and grounds through the engine block.
Thermo-time switch - 2 pin (13621274630) Part of the controller circuit for cold start enrichment.

Motronic 1.0
Coolant temperature switch (12631279722) The switch is an input to the idle control unit.
Coolant temperature sender - white or blue, 2 pin (13621357414) This is the fuel injection ECU sender. The original was white and is NLA. Replacement is the later blue. The blue version simply tightened up the tolerances so the output will always track the ideal value more precisely.
Coolant temperature sender - brown, 1 pin (12621710512) This is the gauge sender.
Thermo-time switch - 2 pin (13621274630) Part of the controller circuit for cold start enrichment.

Motronic 1.1, 1.3
Coolant temperature sender - blue, 2 pin (13621357414) This is the fuel injection ECU sender.
Coolant temperature sender - brown, 1 pin (12621710512) This is the gauge sender.

[95BMWIC]

Also

With idle issues - I would first hook up a vacuum gauge to the intake plennum and see what your readings are and compare those findings to this website: http://www.secondchancegarage.com/public/186.cfm

For the E30 - You should be somewhere between 15-22 in/Hg steady at idle. If it is not at these levels - you have a vacuum leak. A smoke test will help identify where the leak is (a vacuum tester just confirms you have a leak)

I would also check compression readings. Leaky valves will cause irratic idle. (I know- this is what caused mine)

E30 Compression should be from 142 - 156 psi - and you should crank the engine 4 to 5 revolutions when performing the test and the engine should be warm.

[long tall eta]

so my eta is motronic 1.0. which of the 4 sensors in the t-stat housing would cause a high idle (if any) once the coolant reaches normal operating temp.?
question; i did try several icv's that i have. would i need to disconect the battery for the computer to relearn the system after changing icv's and replacing the torn elbow boot?

[95BMWIC]

so my eta is motronic 1.0. which of the 4 sensors in the t-stat housing would cause a high idle (if any) once the coolant reaches normal operating temp.?
question; i did try several icv's that i have. would i need to disconect the battery for the computer to relearn the system after changing icv's and replacing the torn elbow boot?

According to Bentley, Both sensors can effect idle.

Coolant temperature switch (12631279722) The switch is an input to the idle control unit. The switch turns a ground circuit for timing on and off..
The coolant temperature switch can be identified by its two single push on connectors. (1984-1987 325 325e) - To check this use an ohmeter and check for continuity across the switch terminal (remove wires first). At coolant temps below 86F the switch should be open (no continuity). At temps above 118F the switch should close (continuity).

Coolant temperature sender - white or blue, 2 pin (13621357414) This is the fuel injection ECU sender. Depending on connector color measure the resistance across the terminals.

White - Test temperature of 70F - resistance should be around 2100 - 2900


You do not need to reset the system after changing ICV and fixing a torn boot.

[long tall eta]

thank you. great info

[long tall eta]

ok, so here it is. in the never ending mission of reducing my very smooth but very high idle (1000 when cold and slowly building to 1250)when warm i replaced all the t-stat housing sensors. battery disconnected and still high after hooked back up. . swapped out the air flow meter with known working one, still high. replaced the idle control box with known working one, still high.
now this is where it gets interesting. my ecu has an flea-bay chip for years with know problems. i swapped out the ecu with another one and my idle is steady at 750. i put the chipped one back in and guess what? the idle is back to 750. what would cause just unplugging the ecu and plugging it back in to correct the idle? or could it still of been one of the sensors and i just needed to unplug it to be recognized? wouldn't disconnecting the battery have the same affect?