Rough Idle

[felixbobcat]

Looking for some help on diagnosing a rough idle. I just rebuilt my 2.1 to a 2.2, put Mansi big bore heads and his 1.35-1 ratio rockers on and new GoWetsy stainless headers with used stainless muffler and catalytic converter. I also have Mansi injectors that have just a few thousand miles on them. Before the rebuild it did have a rough idle as well but slightly less so.

It revs fine and no sputtering under power. I replaced the spark plug wires to see if that would fix the problem. The Idle control valve appears to be working properly. It vibrates and has continuity. Don’t know if the Idle Control Unit is in good nick though. I don’t get any change in idle speed when the engine is cold or if the AC is turned on.

I haven’t checked fuel pressure since the engine runs fine under power.

My one thought is maybe some water in the fuel tank since it’s been sitting for three months but again it runs fine other then the idle.

I’ve also checked the timing and set it at 35 degrees while running at 3000 RPM. Been thinking of advancing it a little to see if that helps.

Any thoughts?

[Igeo]

Vacuum leak? Worn throttle body?
Can you post up a video of the engine at idle?
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1987 Westfalia 2.1 WBX Manual

[felixbobcat]

I’ve checked for leaks and haven’t found any. That doesn’t mean there isn’t one unfortunately. Movement on the throttle body feels tight. I should check it further though. Will try and record it later.

[dabaron]

disconnect the AFM harness, does the idle improve?
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1991 Vanagon GL Camper
i had no idea i wanted to be a mechanic
"burnin oil and cookin coils" -- Destructo

BiWerks Design, LLC

[MarkWard]

I would unplug the oxygen sensor to put the ECU in open loop. This will give you a true idea of how the engine runs on it's own. The oxygen sensor will try and mask a lean or rich condition.

Next, I would try to isolate the problem to one cylinder if possible. Either by grounding a plug wire or disconnecting and injector with a tach connected. Pay attention to the rpm drop. It should be equal on all 4 cylinders assuming all 4 cylinders are firing equally.

It has also been my experience that while the WBX engine gives smooth performance from the driver's seat. They all idle nervously compared to other engines.
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[felixbobcat]

After a week of what seemed like dead ends I finally found the culprit of the rough idle. I checked the spark plug leads and found one that didn't have any resistance so I installed a new set. Old ones were purchased from BusDepot. Don't recommend them for the sole purpose the leads for one and two cylinder are too short which created a gap leading to loss in resistance. The wire separated from the plug.

However, that didn't solve the problem. It still had a rough idle! I pulled the plugs, they only had a few thousand miles like the leads which where purchased at the same time. Bosch plugs. The plug in number one cylinder had no resistance. It had been firing but not consistently at idle. Replaced them with NGK BP6ET's. Again rough Idle! Gave it rest for the night and went out this morning to look again for something that may cause the idle problem and found that the vacuum hose from the charcoal canister to under the Idle stabilizer valve had been disconnected when I changed the plugs! This created a new vacuum leak that resembled the bad spark plug. Yes, I did check it many times before this morning and even disconnected it while the engine was running to see if that was the problem.

Idles much better now and lost it's intermittent hesitation on revving. Now on to the next problem - the adjusting bolt on the power steering mount just stripped out. At least I know exactly what the problem is this time...

[Igeo]

Good to hear you fixed it. The basics are always good to check first!
I solved an extended cranking issue on hot re-starts with those same NGK plugs.
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1987 Westfalia 2.1 WBX Manual