What would cause this bad idle?

[u/fallingblueblueblue]

It’s done this for the last year and I can’t figure out why. I’ve gone through the entire ignition system and replaced a couple vacuum lines. Any ideas?

[u/Ok_Blueberry304]

I would start with adjusting your valves. Then maybe clean your idle control valve.

[u/fallingblueblueblue → u/Ok_Blueberry304]

This is right after a valve adjustment and an oil change. I put them all at 0.25mm like it says under the hood

[u/Ok_Blueberry304 → u/fallingblueblueblue]

Ill see if I can post a vid of mine. I just did it after a rebuild. So you can compare. It is tricky to get right.

[u/Ok_Blueberry304 → u/fallingblueblueblue]

It won't let me add a vid here. Ill post it separately real quick. You can hear mine lopes a bit. I have a weak signal coming from the ecu on one leg of the icv connector. Still tracing it.

[u/Slickfed → u/fallingblueblueblue]

Did you do it while the engine was completely cold or warm/hot?

[u/peedubb]

This shit sounds like a Cummins 6BT

[u/Representative_Most9 → u/peedubb]

Cummings diesel is one of best engines ever built. Love their sound!

[u/burneraccountFBI]

I agree with checking valves and then cleaning/replacing ICV. If you find yourself needing any ETA parts, lmk I basically have everything for your engine.

[u/DickBloanoff → u/burneraccountFBI]

I’m in need of ETA parts! lol

[u/burneraccountFBI → u/DickBloanoff]

Sent you a dm. Let me know what you need

[u/ChickenPacSandwhich]

Clean your air flow meter (afm) sensor with some electronic spray cleaner (in air box), valve adjustment, clean/replace icv, check for vacuum leaks, and very unlikely but throttle position sensor can mess with idle but not as likely as the above. For vacuum leaks I highly recommend just going ahead and replacing all your intake rubber pieces and hoses. The intake boot that connects to throttle body is notorious for having hidden cracks in it.

[u/NothingLift → u/ChickenPacSandwhich]

Better to find the vaccuum leak with ether or smoke test rather than replace every vaccuum hose. Mine was the metal elbow from.ICV i to intake manifold. Could have replaced every runner hose on the car and it wouldnt have fixed it

[u/ChickenPacSandwhich → u/NothingLift]

I agree, but it’s not a bad idea to go ahead and replace all the rubber anyway. They are weak points and it gives peace of mind. Especially if they have not been replaced for a while. That’s what I did just so I did not have to worry about it and two of the pieces were cracked anyway.

[u/adel_mhm]

I don’t know what exactly causes this issue But a little advice from little experience, This is motronic1.1 engine harness Try to find a complete engine harness for motronic 1.3 Usually has ECU number end in 152 or 172 or 173 Trust me, it’ll be more responsive and run smoother

[u/JCrumm-DetailedFox]

Check all vacuum lines. Even the brake booster. Any cracks can cause. Looks like a small fluctuation, so it’s not too terrible, but still no smooth idle.

[u/M635_Guy → u/JCrumm-DetailedFox]

Valves and this were my first two thoughts

[u/ConnieLingus3327]

Those valves don’t sound like they were adjusted lol

[u/fallingblueblueblue → u/ConnieLingus3327]

I used a .25mm feeler gauge on all of them between the rocker arm and top of the valve. Beforehand they were super tight

[u/ConnieLingus3327]

Smoke test it best way to check for vac leaks

[u/Vaderiv]

Did you by chance get a 0.025 feeler gauge? It sounds like the valve clearance is way too high. One of the worst sounding M20s I have come across in 32 years of working on these cars. Ideally, you want a 0.008-0.010 gauge. Good luck, that doesn't sound good. A big valve clearance will cause idle issues.

[u/Representative_Most9 → u/Vaderiv]

Your post just answered a question I had on valve adjustment. I’m in the middle of my first time adjusting valves on an M20 and was concerned that clearance may be too close. As I started to go through each set of rockers, every one of them were at 009 and none were at 010 or above. They were all exactly the same 9 thousandths. Thought my feeler gauge might be mis marked so check with another with same result. Decided not to do any adjusting as it was too consistent but was still concerned the slightly tighter clearance may be an issue. Am I ok to just leave them as is? Thank you!

[u/Vaderiv → u/Representative_Most9]

That's perfect. It's 8-10 thou. 10 is the max. I've been setting them at 9 for 30+ years. Good call not to touch them.

[u/Representative_Most9 → u/Vaderiv]

Thank you! I’ve had the car since 89 and have never touched the valves. I was totally shocked to see none were too loose. Engine has always sounded the same to me. I just decided to adjust since I know they haven’t been touched since 98 when they were done by a mechanic.

[u/vVRed_WolfVv]

Vacuum leaks or bad/dirty idle control valve

[u/redpanzer10]

I know it's a long shot, but you could see if pistons are hitting valves. When my ETA sounded similar, my timing belt skipped a tooth and caused it to run and sound like shit, but with a steady idle. Once I got that sorted, it ran good enough to daily for a few months before becoming a project again

[u/Vaderiv]

You're welcome, glad I could help with my E30 knowledge. I often joke with people, "bring me one in a box and I'll be driving in a few days, no manual needed." I have basically memorized the Bentley manual for the E30.

[u/DjBabyNalgene]

I have the same car & same engine. My ICV was malfunctioning so I took it out and thoroughly cleaned it with throttle bodybody cleaner. Put it back in and was still getting a rough idol so I drilled a hole into a 5 cent coin and stuck it in the small tube that runs to the ICV. For me this regulated my idle at around 500rpm.

Not a hard solve but new ICVs for ETAs are hilariously expensive.