Post-interference head rebuilt E30/M20; now poor idle...

[moapys]

Got the mechanicals squared away, and the lapped valves sound/feel good, and pass leakdown testing - but the idle is lumpy. I'd suspected vacuum (leak), but cannot find with smoke test.

The stomp-test (late to consider, since no CEL was illuminated) yields a 1-2-2-2 code, indicated "Lambda 1". This still suggests any number of vacuum/sensor/connection possibilities. 'Any one have any pointers or experince in solved cases? THX

[jlevie]

Was the smoke test done properly with a pro-type system that uses long persistence oil smoke?

[redlightpete]

Have you adjusted the valves since you installed the head on the motor? If they were adjusted before the head install, they'll be too tight.

[moapys]

Continued thanks, guys - I'm seeking someone with a proper smoke test rig, as my homebrew set-up hasn't evidenced any vacuum leaks. Hope to get that arranged soon! Meanwhile, I'll do a re-adjust on the eccentrics this weekend, and report back if that has made a difference.

[moapys]

Well - the latest...: I cleared the 1222 code (it was a holdover from past vacuum noodling - last several starts/trips resulted in no (eg 1444) code. Alas, so much for that red herring... I did re-adjust the valves, stone cold, they were a bit tight, so put them back to a solid .010 - and checked both ends of the rockers for .01 / .007 consistency...all good. I even checed the 02 sensor for good measure; proper waveform and voltage levels.

Finally, I took it to an independent ASE shop for a real smoke test - which they claimed it passed "with flying colors". Since the lumpy idle persists, I am throwing in the shop-towel and taking it to a specialist. I only hope they read my litany of tests run...versus assuming that they're starting-from scratch :-( ...I'll be sure to post the results (beyond wallet depletion) once received!

[jlevie]

When were ignition wires, etc., last changed? 150k is as long as i will trust those parts. What plugs are you using? The best alternative to the NLA Bosch plugs is NGK ZGR5A. If the engine has 150k or more on it, consider having the injectors professionally cleaned, rebuilt and flow tested. i use RC Engineering for injectors.

[5Toes]

yes on injectors. my last set of m20b25 ones I had done, some only flowed 15% of what they should have

pics before



after:

[moapys]

Poor idle...occurred immediately after rebuild, so...

...would wonder how injectors would have been impacted. Further, in sequentially removing plug wires to gauge impact to idle, each (degradation) was identical: Should there have been a balky injector, 'seems that cylinder's disabling would have shown less impact <?>.

I like the theory, and if it had occurred either over time or suddenly non-coincident with the valvetrain issue... 'Still, much obliged for the noodling on this, I'll chase all rabbits until the good shop in town calls me back!

[moapys]

Post-head rework (M20); seeking Indie in INDY...

All - per the above, I began looking for e30 expertise in Indianapolis: I've now tried Merkle (dissatisfied/no-help), Mikar (great guys; too busy) - and it looks like I'm relegated to Reggies...who is well respected by the racers, but I suspect will be VERY costly as a "boutique shop"...

Does anyone have any favorite BMW service experts in the greater Indianapolis area? It's quite driveable - but wouldn't relish a trip to Chicago unless my only recourse. 'Continued thanks, guys.

[modernist]

old injectors get clogged with carbon and other crap. MEPEH does a great job, I bought some from him and they've been great so far. if you don't know when the last time your ignition system was serviced, replace your distributor cap, rotor, spark plugs, and spark plug loom. try cleaning out your ICV with some carb cleaner. check for corrosion in the C191 connector.