Idle up and down ?

[318wa]

Just recently bought my first e30. Runs good but sometimes while idleing it revs up and down. Is this common and can anyone let me know what might be up and what I can do to fix it.

[mmmjboner]

Idle Control Valve (ICV) might be faulty, or the pintle could be dirty.

[Garageaholic]

I have the same problem. I thought it was the reference or crank sensor!

[KenC]

it's probably a vacuum leak

[jlevie]

A bouncing idle could be any, or a combination, of; intake leak, sticky ICV, bad AFM, or bad TPS. In rare cases a flaky CPS can be a contributor, though that usually results in other problems off idle.

My approach is to pull everything, clean the throttle body/AFM/ICV until they are operating freely, inspect and replace any cracked hoses, and check the operation of the TPS and AFM. Then I'll reassemble and verify the idle stop and TPS adjustment. That process will also tell if the ICV is working.

Note that an intake leak that is easy to miss can be in the vacuum circuit to the brake booster.

[Garageaholic]

Are there any techniques to check for vacuum leaks?!??

[euroshark]

Some people will spray ether or starter fluid around the hose connections, some use soapy water. Make sure to tighten all of the hose clamps. Loose clamps were the reason I got my E30 for $250!!

That said, vacuum leakes generally don't make a bouncy idle, they make a rough idle, and maybe some erratic power pulsing while driving. If the idle has a rythmic bounce, keep reading.

Check the fuse(s) that control the ICV. If the fuse is ok, you can stimulate the ICV manually to see if it works. Just do this with some small jumper wires on an old car battery (or another 12 volt source). If you hear it click when you apply electricity, it works. Some cars had an idle control module, a little computer that tells the ICV what to do. In my 533i the ICV and ICM are on the same fuse... and when it failed (ugh, old ceramic style) I couldn't even tell by looking at it! If both the ICV and ICM are ok, check your oxygen sensor plugs (there should be one in the engine compartment, and one further down the line, under the car) juct unplug them and reconnect them. Sometimes that will do the trick if they are malfunctioning due to corrosion. If you unplug the oxygen sensor and your idle improves, you need to replace the sensor.

Lastly, since the TPS and AFM really won't make your idle surge unless they are seriously screwed... and in that case, you'd notice other drivability issues; check the coolant temperature switch on the water manifold at the front of the motor. Its in that cluster of sensors, and it has two male connector prongs that stick out of the top. This switch tells the ICV when to close, and if it is malfunctioning, you will surge all day long! Try unplugging one or both wires that connect to it, and if the idle goes up (about 1250rpm in my 533i) then it's bad. You can solder where the male prongs connect to the sensor, as this is usually the reason they fail... the connections just get loose and then eventually break. You need to make sure to get a lot of acid paste down under and around them though, or your soldering will not do you any good! If you need more help, or pictures of anything, let me know!

Good luck

[porsche gt1]

Some people will spray ether or starter fluid around the hose connections, some use soapy water. Make sure to tighten all of the hose clamps. Loose clamps were the reason I got my E30 for $250!!

That said, vacuum leakes generally don't make a bouncy idle, they make a rough idle, and maybe some erratic power pulsing while driving. If the idle has a rythmic bounce, keep reading.

Check the fuse(s) that control the ICV. If the fuse is ok, you can stimulate the ICV manually to see if it works. Just do this with some small jumper wires on an old car battery (or another 12 volt source). If you hear it click when you apply electricity, it works. Some cars had an idle control module, a little computer that tells the ICV what to do. In my 533i the ICV and ICM are on the same fuse... and when it failed (ugh, old ceramic style) I couldn't even tell by looking at it! If both the ICV and ICM are ok, check your oxygen sensor plugs (there should be one in the engine compartment, and one further down the line, under the car) juct unplug them and reconnect them. Sometimes that will do the trick if they are malfunctioning due to corrosion. If you unplug the oxygen sensor and your idle improves, you need to replace the sensor.

Lastly, since the TPS and AFM really won't make your idle surge unless they are seriously screwed... and in that case, you'd notice other drivability issues; check the coolant temperature switch on the water manifold at the front of the motor. Its in that cluster of sensors, and it has two male connector prongs that stick out of the top. This switch tells the ICV when to close, and if it is malfunctioning, you will surge all day long! Try unplugging one or both wires that connect to it, and if the idle goes up (about 1250rpm in my 533i) then it's bad. You can solder where the male prongs connect to the sensor, as this is usually the reason they fail... the connections just get loose and then eventually break. You need to make sure to get a lot of acid paste down under and around them though, or your soldering will not do you any good! If you need more help, or pictures of anything, let me know!

Good luck

2x on this,

[318wa]

Im not too familiar with these cars so any pictures would help, thanks.

[318wa]

I dont know if this would help anybody narrow down the program but the mpg gage also floats up and down.

[volgapower]

i had the same problem and it was a vacuum leak. also check the legendary blue water sensor... :)