How big of a vacuum leak would this be?

[I6V8]

My smoke tester surfaced a vacuum leak from my throttle plate shaft needle bearings. It doesn't look big but for the M20 owners here who fixed this in the past, how much of an improvement did replacing the shaft bearings make to your idle quality?

Car is an '89 325is. Rest of the engine has 30K miles on a deck to pan rebuild with a refreshed head, recently adjusted valves to .08" and .09" and all other remaining vacuum leaks were fixed (oil filler cap, half moons, elbows etc)

[88Sedan]

I fully rebuilt my throttle body solely because those bearings were a massive leak on my car. It was like blowing through a straw. Extracting the old ones meant buying a blind bearing puller with 8mm attachment.

I carefully laid out parts as I disassembled and took pictures just in case. I ended up having success by carefully heating around the bearing bore and let many repeated attempts with the slide hammer.

I recommend leaving yourself the time and mental capacity to be patient with pulling the bearings as it wasnt a quick thing for myself. I kept reheating carefully as to not crack the aluminu. Once everything was out and thoroughly cleaned I inserted the new double seal bearings using a light amount of black rtv to seal any potential crevices.

Because my car had many vacuum leaks repaired at the same time I cannot comment on the direct effect this had. I too adjusted my valves to .009" to help quiet the valvetrain down, but supposedly . 010" is better for idle quality .

[I6V8]

I fully rebuilt my throttle body solely because those bearings were a massive leak on my car. It was like blowing through a straw. Extracting the old ones meant buying a blind bearing puller with 8mm attachment.

I carefully laid out parts as I disassembled and took pictures just in case. I ended up having success by carefully heating around the bearing bore and let many repeated attempts with the slide hammer.

I recommend leaving yourself the time and mental capacity to be patient with pulling the bearings as it wasnt a quick thing for myself. I kept reheating carefully as to not crack the aluminu. Once everything was out and thoroughly cleaned I inserted the new double seal bearings using a light amount of black rtv to seal any potential crevices.

Because my car had many vacuum leaks repaired at the same time I cannot comment on the direct effect this had. I too adjusted my valves to .009" to help quiet the valvetrain down, but supposedly . 010" is better for idle quality .

Thanks. Is your idle completely smooth now?

I just slightly retightened the intake manifold nuts after getting a small noise when pushing down on the plenum. That noise is gone.

I didn't get any visible leaks before but the vibration from the engine might have created pulsing mini-leaks that weren't detectable with the engine off.

Smoked tested her again after and can still see the leak at the taller pivot point shaft on the TB, so the one closer to you when you stand on the driver side. Trying to decide if this is worth the trouble.

My 2 symptoms are: a short stumble or hesitation off-idle when you open the throttle plate quickly when the engine is hot and the exhaust fumes smell rich at idle. The other is, during engine warmup, the motor noticeably vibrates more in neural and parked, especially around 2K RPM. Once the thermostat opens, the vibration smooths out.

I already replaced the blue temp sensor, car is running OEM green tops with a SSSquid chip for that setup on 91 gas.

[88Sedan]

My idle has greatly improved but I wouldn't say it's perfect. Mine has this periodic lumpiness I haven't figured out yet but I would say it's minor. It's cyclical so I checked the valves 3X to feel confident about it.

When I replaced the plugs I think I got irridium or platinum plugs and that might be throwing the ignition off a little. I just did an entire reseal of my engine sans HG. New crank sensor, cap/rotor, and I multimeter-checked all the dme wiring.

I have 2 good afms, neither made any difference. Recently realized the icv hose that previously was good now looked bad suddenly, so I replaced it and that helped the idle more. Car starts immediately and otherwise sounds good. After an engine rev it finds idle quickly and smoothly, no hunting idle at all for me. I'll admit I still have to smoke test, check plug wires, and lastly if it's not perfect fuel injectors. These motors are finicky when it comes to vacuum.

[I6V8]

Sounds similar to my idle quality. During cold operation (in SoCal at 60F+ ambient temps), I did get a weird 200rpm up and down movement when holding the throttle steady at 1800rpm along with the weird vibration that felt like it wasn't firing fully on all cylinders. In another thread, someone said that was indicative of a rich mixture during open loop operation which matches the exhaust gas smell I'm getting.

So after completing the work this morning, I decided to reset my ECU and that did smooth out the hot idle a bit more on the drive after. I turned my afm bypass screw 2 extra turns out over the factory setting to lean things out a bit at idle before the O2 sensor takes over. Not sure if the SSSquid chip richens the sub 140F A/F mixture so I'll just drive like this for a bit now and see what happens.

Maybe try the recommended Bosch replacement NGK plugs and make sure to gap them correctly. I also hear the ignition wires are quite finicky and like to short out. Years ago, this old school mechanic would touch each wire and if he got shocked, replaced just that one, lol. I don't necessarily recommend that method but he said he found bad wires on M40s and M20s pretty often.

[88Sedan]

Hmm the 200rpm fluctuation is interesting, I never had that with my car. I have read that playing with the AFM screw is risky so I never have/would play with it until I really felt I needed to.

To clarify, you set your clearances to .009"and .010" correct? I think you put the decimal in the wrong place in the OP.

The throttle body rebuild is easy conceptually if you are diligent at taking pictures etc (note the position of the butterfly valve as it only fits 1 way/1 orientation). Like mentioned you have to exercise patience with the bearings if you don't want to damage anything.

If you remove your TB and wipe/clean the area around that shaft, and make sure no ones looking haha, put your mouth on it and blow and it'll give you an idea of how bad it is. Mine was really bad! I also think this was responsible for how filthy my intake runners were, the PO put thousands of miles with this and other leaking vacuum sources. If you have any e30 buddies I'd be tempted to ask them to swap AFMs for a few hours to see what/if anything changes.

[I6V8]

Blowing on shafts and listen for noises? At that point, what are we NOT prepared to do to get these motors to idle smoothly, lol?

Based on your findings, these needle bearing leaks could be pretty significant and are probably fairly common.

I wonder if it's at least possible to seal up the bottom needle bearing with marine grease where the shaft plugs into the TPS?

Another question: when you had the TB off and apart, how was the first shaft and spring near the inlet mounted to the TB? Is there a 3rd bearing and possible entry point for unmeasured air?

Regarding the valves, I definitely had the decimal points wrong but the lash is set to 0.008 and 0.009.

I don't believe dirt in the intake has anything to do with the vacuum leaks. Some oil getting sucked through the rocker cover vent hose is normal and that can build up and get caked on over the years. If it's excessive, however, it could be an indication that there's too much crank case pressure from blowby gasses due to piston ring wear. When you change the spark plugs to the better NGK ones, maybe put a borescope camera in there to see if the cylinder walls all look healthy.

[88Sedan]

There are only 2 bearings in the TB, but the brake booster nipples can become loose. I tapped threads and changed the check valve setup and hoses. What used to be 2 press in nipples is now one threaded one and one plug. One TB stud is stationary if I recall correctly. The third large nipple for the icv I held in place with loctite retaining compound.

[packratbimmer]

Great thread! Where are you getting new bearings? Thanks

[88Sedan]

These are dual sealed vs the OE single sealed.
INA HK0812 -2RS-FPM-DK-B-L271

Cheapest place I found was fleebay.

[packratbimmer]

Great info on the bearings/seals! Concerning idle, I have also found that the throttle plate clearance AND its relationship to the throttle switch are critical. The Bentley manual has the specs and procedure. One thing to avoid is adjusting the throttle plate AFTER the throttle switch because there is a chance that the switch will open at the wrong time or not at all upon the return of the throttle to rest.

[I6V8]

There are only 2 bearings in the TB, but the brake booster nipples can become loose. I tapped threads and changed the check valve setup and hoses. What used to be 2 press in nipples is now one threaded one and one plug. One TB stud is stationary if I recall correctly. The third large nipple for the icv I held in place with loctite retaining compound.

I'd sealed the elbows months ago and smoke isn't coming up but read somewhere that when the check valve is closed with the engine off, you can't see leaks behind the valve in the brake booster or lines with a smoke test. Same with the evap canister check valve.

I ordered a new brake booster check valve and will test the evap circuit one but it's noteworthy that my idle improved a lot after lightly tightening the intake manifold nuts and resetting the ECU.

[I6V8]

Great info on the bearings/seals! Concerning idle, I have also found that the throttle plate clearance AND its relationship to the throttle switch are critical. The Bentley manual has the specs and procedure. One thing to avoid is adjusting the throttle plate AFTER the throttle switch because there is a chance that the switch will open at the wrong time or not at all upon the return of the throttle to rest.

Yes. JLevie shared instructions somewhere on here for calibrating the idle after the throttle plate screw has been tempered with. One of his posts said that relying on just the click isn't a reliable way to determine that the ECU gets the idle signal from the TPS. I found out after to turning the screw out a bit to raise the idle (600 is low). Hooked up a speaker wire with connectors for spades that fit right on the TPS terminals and checked for continuity with a MM and sure enough, didn't get a beep despite hearing the click. What I can't say for certain is if JLevies instructions work for late model TB boots with the extra connection into the brake booster vacuum lines before the throttle platw so I just left it and decided to focus on getting it to idle smoothly at 600.

[packratbimmer]

The 1st step is to set up the throttle plate clearance ( distance between the throttle plate and the throttle opening), then set the "gap" so that the switch closes shortly before the plate lever hits the stop.

https://www.r3vlimited.com/board/forum/e30-technical-forums/engine-drivetrain/m20/173413-proper-throttle-adjusting

[noid]

Throttle body bearings:

With all other vacuum leaks sorted, you can generally forgo the bearings. There is a good chance the plastic under the spring will break during disassembly/reassembly, and at that point the TB becomes trash.

This is a o2 controlled fuel injected system, so unmetered air gets compensated for; as long as its relatively consistent and minor; which in this case it is. With a healthy TPS oring, it really is only the top bearing that usually has a minor leak.

https://www.rtsauto.com/vacuum-leak-location-on-e30-throttle-body-m20/

Idle control:

Again, what we are talking about here is a Motronics fuel injection system, idle is controlled by the ECU and subsequently the ICV, not mechanically. Trying to adjust idle by way of the AFM idle screw or by way of the TB screw is not the correct way of going about this.

There is a factory depth stamp on every AFM that indicates the depth that the idle screw should be; set it back to that factory depth.

If the AFM has been messed with in any other way, continue to set it back to these perimeters:

https://www.rtsauto.com/how-to-test-e30-bosch-afm-bench-test/

ICV:

Ensure a proper functioning ICV by way of these tests:

https://www.rtsauto.com/how-to-test-e30-icv-idle-control-valve-m20-engine/

Throttle plate and TPS adjustment:

The throttle plate should be in a completely closed position when at rest; again, do not attempt to adjust idle by making the throttle plate stay slightly open.

Test and adjust the TPS as indicated here:

https://www.rtsauto.com/e30-m20-tps-throttle-position-sensor-adjustment-and-installation/

The E30 TPS is very prone to intermittent faults at this age due to cracks in the solder joints internally.