I’m new to E30s and DIY on old cars so I really tried to read threads and do a lot of normal fixes before posting. You guys are smart and busy. But this issue seems unique to all the idle problems I’ve been reading about. Maybe some big brains out there can crack the case.
I bought the car with 165k and have added 5k. It was very well kept and runs strong. Since I’ve had it the idle has always been just above 500. When the car warms up, it starts to drop and catch itself a bit making the engine shake enough to feel it a little inside the car. Not a ton, but it’s there. Sometimes at lights the check engine light will come on after a shake. A quick rev will turn the light off. An off idle throttle blip drops the RPMs initially but it recovers quickly and will rev perfectly from there. Gas mileage has remained at 20-21mph no matter how I drive. I’m new to older cars but the idle exhaust seems rich. No black smoke or anything extreme. Just reminds me of the smell and sound of an old American muscle car. Turning the AC on temporarily raises the idle and smooths out the engine but it goes back to 500-600 quickly and gets rough again. I’ve read a lot about idle that revs up and down or that is too high, but this seems totally different.
Here’s what I’ve done to chase the issue:
- New paper air filter
- Removed air box and made sure nothing was dirty or stuck
- Removed all rubber going to the throttle body and checked for leaks
- Replaced one hose under the TB from 1988 with a split
- Cleaned the TB and ICV really well
- Checked to make sure the ICV buzzes
- New plugs. The old ones were well worn but perfect brown
- New rotor and distributor cap
Also did some non-related maintenance stuff:
- 50/20 oil change
- Radiator flush with 50/50 blue coolant and distilled water
- Replaced fuel filter
None of the intake cleaning and repair changed anything. The new distributor/cap/plugs made it run smoother and added some nice low end torque, but the idle issue is exactly the same.
There’s one other thing that might be throwing it off: The car was converted from automatic to manual with a rebuilt stock 5-speed. It had cruise control that the seller said stopped working after the conversion. I wonder if engines with automatics had a different idle setup that has trouble with the manual clutch. As soon as the clutch is engaged and I creep along with no throttle it calms down.
I plan to do a full interior restore and drive this guy all the time. I’m willing to invest in making it right for everyday use. The people I’ve brought it to so far either don’t work on old BMWs or they rig up old stuff and tell me I should be lucky it starts every time. So I turn to you! Help me get this fella running like it should.
I bought the car with 165k and have added 5k. It was very well kept and runs strong. Since I’ve had it the idle has always been just above 500. When the car warms up, it starts to drop and catch itself a bit making the engine shake enough to feel it a little inside the car. Not a ton, but it’s there. Sometimes at lights the check engine light will come on after a shake. A quick rev will turn the light off. An off idle throttle blip drops the RPMs initially but it recovers quickly and will rev perfectly from there. Gas mileage has remained at 20-21mph no matter how I drive. I’m new to older cars but the idle exhaust seems rich. No black smoke or anything extreme. Just reminds me of the smell and sound of an old American muscle car. Turning the AC on temporarily raises the idle and smooths out the engine but it goes back to 500-600 quickly and gets rough again. I’ve read a lot about idle that revs up and down or that is too high, but this seems totally different.
Here’s what I’ve done to chase the issue:
- New paper air filter
- Removed air box and made sure nothing was dirty or stuck
- Removed all rubber going to the throttle body and checked for leaks
- Replaced one hose under the TB from 1988 with a split
- Cleaned the TB and ICV really well
- Checked to make sure the ICV buzzes
- New plugs. The old ones were well worn but perfect brown
- New rotor and distributor cap
Also did some non-related maintenance stuff:
- 50/20 oil change
- Radiator flush with 50/50 blue coolant and distilled water
- Replaced fuel filter
None of the intake cleaning and repair changed anything. The new distributor/cap/plugs made it run smoother and added some nice low end torque, but the idle issue is exactly the same.
There’s one other thing that might be throwing it off: The car was converted from automatic to manual with a rebuilt stock 5-speed. It had cruise control that the seller said stopped working after the conversion. I wonder if engines with automatics had a different idle setup that has trouble with the manual clutch. As soon as the clutch is engaged and I creep along with no throttle it calms down.
I plan to do a full interior restore and drive this guy all the time. I’m willing to invest in making it right for everyday use. The people I’ve brought it to so far either don’t work on old BMWs or they rig up old stuff and tell me I should be lucky it starts every time. So I turn to you! Help me get this fella running like it should.
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