Idle issue; low but steady. Help?

[dr.strangelove]

i hate posting about idle issues, but it seems i have a little different of a situation.

My idle was really erratic, and i eventually found out that the throttle body screw was adjusted wrong. readjusted it, cleaned out the ICV, the AFM, and the throttle body. Reinstalled everything and the idle was somewhat steady.

I did however notice that the idle was far lower than it should've been. It was sitting around 500 rpms or so but steady. I decided that since i had a spare cap and rotor (only 8 months old) and a set of newer wires Bosch 7mm, that i would change that out to hopefully help out the idle. I also checked the FPR for gasoline smell in the vacuum line, and it smells of course so i know i will be replacing that soon. The wires, cap and rotor helped but not much. I reconnected the battery, and have driven the car roughly 40 minutes since the reset. The car idles around 550 or so, and this is not kosher.

Keep in mind that this car is a auto to 5 swap car, and also a 1991 325iX. this car previous to the 5 speed swap had the similarly low idle. The car calls for a T style ICV valve with the extra appendage to the vacuum lines coming from the booster. Since i did not have a good condition intake bellow for that application, i installed an earlier L style ICV and the appropriate intake bellow. The ICV does buzz btw.

I am really curious as to what could be the problem here. I will be ordering a brand new coolant temp sensor (blue bosch), an 3 bar FPR (bosch), a set of 6 new bosch W8LCR copper spark plugs, a new intake bellow, a fuel filter (mahle) and that vacuum line that runs to the charcoal canister from under the throttle body.

Am i missing anything? anything that i should not have to get?

If anyone can inform me as to the possible cause for this low yet steady idle, i would truly appreciate it.

Also i am trying to think of a fuel additive that might help in cleaning the fuel system. Any opinions on the 3M, Redline, or Seafoam products?

[jlevie]

It could well be that the throttle stop and TPS aren't correctly adjusted and/or that the idle switch in the TPS is bad. Check the TPS to ensure that the idle & WOT switches operate at each end of travel of the TPS with a test light & battery or ohmmeter. Since the TPS and throttle may be out of adjustment, I'd recommend removing the TPS for this test.

The adjustment of the throttle & TPS is done by (from memory, check the Bentley):

1) Run the engine until it reaches normal operating temperature.

2) Disconnect the ICV and adjust the throttle stop for an idle of 950rpm.

3) Shut down the engine and adjust the TPs so that the idle switch closes (as shown by a test light or ohmmeter) when the throttle is 0.020-0.040" off the idle stop.

4) Reconnect the ICV and the idle should be ~750rpm.

If the idle is unstable after this, the ICV is bad, you have an intake leak, or there's a problem with the AFM.

[dr.strangelove]

When you mention step 2, you mean, while the car is running (at idle), disconnect the connector to the ICV, and adjust the throttle body screw till the car idles at 950 (open the door), right? or are you telling me to completely remove the ICV from the system?

[jlevie]

I mean disconnect the electrical connector to the ICV.

[dr.strangelove]

ok, so here is an update. I went ahead and adjusted the throttle stop to .0015". I adjusted the TPS properly (idle at .024"), and went to start the car. at first the idle was decent, then would slowly start to drop back down to around 500 or so. If i disconnect the ICV, there is no change in idle, and i am starting to think that it is either bad, or something else is not kosher. I know that the metal fittings on the throttle body are slightly loose, so i plan to JB weld those back into place.

I have take the liberty to order a brand new coolant temp sensor (blue bosch), an 3 bar FPR (bosch), a set of 6 new bosch W8LCR copper spark plugs, a new intake bellow, a fuel filter (mahle), the vacuum line that runs to the charcoal canister from under the throttle body, and the ventilation tube from the head to the throttle body if i'm on track. I have two spare T style ICVs, and i hope that this will be the fix. As for the spark plugs, i have not changed out what the PO had in there, but hopefully this ensemble of parts does the trick.

any other tips as to what else i should check?

[jlevie]

ok, so here is an update. I went ahead and adjusted the throttle stop to .0015". I adjusted the TPS properly (idle at .024"), and went to start the car. at first the idle was decent, then would slowly start to drop back down to around 500 or so. If i disconnect the ICV, there is no change in idle, and i am starting to think that it is either bad, or something else is not kosher. I know that the metal fittings on the throttle body are slightly loose, so i plan to JB weld those back into place.

The correct adjustment of the throttle stop is that which results in an idle of 950rpm on an engine at normal temperature and with the ICV disconnected. I have no idea where you are coming up with the .0015".

Assuming that the idle switch in the TPS is working and closed when the throttle is against the stop, the idle should fall to 750 when you reconnect the ICV. If that doesn't happen, the ICV isn't working.

JBweld is a good way to fix the nipples that were pressed into the throttle body. just make sure to throughly clean the nipple and bore with Acetone before applying the JBweld.

[dr.strangelove]

what are you turning or adjusting to get the 950rpm. I went according to the basic throttle adjustment in the bentley, on page 38 section 6. they mention that the plate should have a clearance of .0015" from the throttle body housing. Maybe you can educate me on this throttle stop, as i adjusted the screw with the plastic security cap on it behind the mechanism per the bentley.

[jlevie]

The throttle and cruise cables attach to the throttle quadrant at the top of the throttle body. A part of that quadrant sticks down and closes against the idle speed screw. That screw runs fore/aft and is on the intake side of the throttle body.

[dr.strangelove]

yeah, that little allen head stud screw. I adjusted that just like the bentley states, but for the life of me, i cannot find anything that shows the method that you have listed above.

[dr.strangelove]

little update. installed the new spark plugs, new FPR, new fuel filter, and coolant temp sensor. Plan to do the vacuum hoses in the next day or two, but the idle is still really low right around the 550 mark. i wonder if the O2 sensor, valve adjustment, and maybe freshening up the injectors would help any.

and jlevie, any updates one where you got the information on the set at 950rpm, and install ICV info?

[dr.strangelove]

I tested the voltage on the ICV, and the center reads 12v, the center to each of the outers is a hair under 10v on one, and 4 volts on the other. Could this be a bad ecu? resistance on the ICV is good, and all the components above have been replaced. I am going to be ordering the appropriate vacuum hoses, and i plan to do the throttle body next available chance.

[dr.strangelove]

ok i just read up about setting idle some more on the service manual. basically, you need to simulate idle position for the TPS.

Have your car running at temp, at idle.

if you disconnect the TPS and you have the harness in hand look at it. looking at the side that connects to the TPS, you should have three female connectors. run a lead from the center one to the right one (should simulate the idle position as it would be on the TPS).

For further clarification, you can check your bentley and make sure that the lead is running from where pin 2 and pin 18 would connect to.

then set your idle to 750 +/- 20 rpm. Once you have done this, you should probably readjust your TPS to reflect that measurement.

that is what i read on the service manual, and it seems to me that the "special tool" does just as i say since that would be what the computer would want.

i will do this in the next day or two and confirm how this works.

Keep in mind that all vacuum leaks and such should be sorted out and all components should be in good working order.