Help! Car won't idle anymore

[Nick_S]

So I just recently pulled the engine/transmission (M50NV/G240) out to do a new clutch. While out it got brand new flywheel,clutch,PP, TOB, new seals and bushing and the engine got a new rear main and crank seal and thermostat. I also cleaned it up pretty well. Once back in the car, it will crank just fine and start but won't stay idling. If I keep the RPM's around 1500 it will run but with a slight miss. It's driveable but stumbles under load and more than 1/2 throttle. Mind you before I pulled it out, the engine was running perfectly.



In trouble shooting I have tried 2 known good working DME's, multiple fuel pump relays and I have checked all connections, replaced fuel lines, checked for vacuum leaks and can't find any real smoking gun.



The one interesting bit I have found is I tried to jump the fuel pump relay with a wire from 30 to 87, the car won't fire which I find odd. I had done this when I first did the swap in tracking down an issue and it fired up fine. Once the pump relay is reinstalled it will fire over just fine. Electrical issues are one of my main weak points with cars so I'm a bit stuck.

[e30austin]

Make sure that the "turkey neck", underneath the manifold, on the back side, didn't come out. Sounds like you have a giant vacuum leak.

[Nick_S]

It's def connected. While idling (with a quarter wedged to keep it 1500rpm) I sprayed brake clean around the intake and it didn't rev up or change. It's acting like it has a giant vacuum leak but I can't detect one.

[e30austin]

Unplug your MAF and see if that changes anything.

[Nick_S]

Unplug your MAF and see if that changes anything.

It doesn't

[e30austin]

Does it throw a CEL? Did you take the manifold off the engine for any reason? If you reversed any of the connectors under the manifold, that would certainly cause an issue.

[Nick_S]

Sadly the CEL is not hooked up..probably should get on that. Friend of mine has an OBD1 scanner hes bringing down this week to scan it. I did take the manifold off (twice now). First time was to ease the engine out, then I realized I put the heater hoses to the core backwards so I pulled it again and double checked all connectors and replaced the rubber fuel lines under the manifold. I didn't unhook the cam/crank sensors but in cleaning the engine I did remove the crank position sensor and even though it's back in the location and tightened down. I'm wondering if it was damaged somehow.

[e30austin]

Is it the original crank sensor? You should perform a resistance test on it. Within 10% of ~565ohms is specification.

I still say some sort of giant vacuum leak. Throttle position sensor and ICV connectors get reversed?

[Nick_S]

Is it the original crank sensor? You should perform a resistance test on it. Within 10% of ~565ohms is specification.

I still say some sort of giant vacuum leak. Throttle position sensor and ICV connectors get reversed?

The CPS was replaced with a new OEM one when I initially did the swap but that has been 5 years. Is the TPS able to plug into the ICV? If so I'll give that a check tonight.

[e30austin]

They are both three pin and almost the same length. I've seen it happen once before. Your friend with the diagnostic tool should hopefully point you in the right direction.

[Nick_S]

They are both three pin and almost the same length. I've seen it happen once before. Your friend with the diagnostic tool should hopefully point you in the right direction.

Interesting. It's quite possible that it may have happened. I didn't have them labeled. I'll give it a check tonight. If you're correct I'm going to mail you a 6 pack.

[Nick_S]

They are both three pin and almost the same length. I've seen it happen once before. Your friend with the diagnostic tool should hopefully point you in the right direction.

Wasn't the sensors. I still had the marking on the ICV harness. My main ground strap was loose. Tightened it and no change with the way it runs. I checked the crank position sensor and the black plastic piece seemed a bit loose, not sure if that would cause some issues but I don't recall it being like that before. Going to order in a new one or try and track down a good one.

[e30austin]

I see you ordered a Meyle (Chinese) unit when you did the swap, five years ago. I would change it to a genuine unit - they will last the longest. However, generally, when they fail, they just don't work.

I would also check the fuel pressure (Bentley lists the spec), and if you haven't done it lately, install a new, quality, fuel filter. I had a similar issue with a customer car, and it ended up having a completely clogged fuel filter.

[Nick_S]

I see you ordered a Meyle (Chinese) unit when you did the swap, five years ago. I would change it to a genuine unit - they will last the longest. However, generally, when they fail, they just don't work.

I would also check the fuel pressure (Bentley lists the spec), and if you haven't done it lately, install a new, quality, fuel filter. I had a similar issue with a customer car, and it ended up having a completely clogged fuel filter.

You're correct, my memory is a bit off from then. I was under the impression it was sort of work or don't with those. Was going to put a gauge on this weekend as it seems like a fuel delivery issue. I do actually have a brand new fuel filter sitting on my bench. I'll give that a whirl first.

[Nick_S]

A while back a friend of mine had mentioned to not rotate the crank backwards as it can sometimes jump time. I have personally never heard this but there's a lot I don't know. Anytime I was doing anything that would cause rotation I had a socket and ratchet bracing the crank so I could tightening or loosen BUT there's a chance it may have rotated back slightly and possibly jumped a tooth. Does this sound feasible to anyone? If so how can I check to make sure it's in time? My bentley manual was lost somewhere in my move unfortunately.