Replaced intake manifold gasket and now the engine starts but won't run

[knick_knack]

I must have made a mistake somewhere along the way. Hopefully a description will allow someone to help me to narrow the list of possible culprits.

My engine wasn't idling very well, and when left at the same RPM for too long (thirty seconds or so) the CEL came on.

I discovered that spraying carb cleaner around the intake manifold gasket improved the idle, so I set about to change the intake manifold gasket. To take off the intake manifold I had to remove the airbox (which includes the ICV and connectors for the ICV and AFM), the TPS connector, and the vacuum lines connected to the throttle assembly. At this point I was able to remove the 12 nuts holding the intake manifold on, but to get the manifold off cleanly I ended up also removing the coolant bleeder valve, one of the hoses into the coolant thermostat housing (had to drain the coolant to do so), and the fuel pressure regulator (not helpful, definitely a mistake).

After replacing the gasket and reattaching the manifold and everything else that I disconnected or removed, the car doesn't run without a lot of throttle. It starts but immediately dies if I don't give it gas. If I give it lots of throttle I can keep it running at a high rpm, but not below 2500 or so.

So here is my current list of possible culprits:
- Any of the vacuum tubes that I removed and reattached
- Connection to the ICV, AFM, or TPS
- I could have damaged one of the sensors on the fuel rail
- I could have improperly reattached the fuel pressure regulator. Fuel came out, which means air got it. Does it need to be bled?


I figure its one of those issues as the type of problem seems like it would be cause by an issue with fuel or electrical, but just in case I'm also considering these possibilities:
- I poorly seated the oil return tube from intake manifold (apparently there is supposed to be a washer under the spring). Could this be a big enough air leak to cause the problems I'm having?
- coolant system wasn't refilled correctly (there is no way it could cause these problems, right?)


Can anyone help me narrow down the likely causes?

[digger]

Fuel lines to fpr mixed up?

[knick_knack]

I didn't actually remove any of the lines going into the fpr - I just removed the two bolts that hold it on and lifted it off its seat on the fuel rail.

[Bullet Ride]

Fuel rail doesn't need to be bled, any air just gets pushed through the return line.

The fact that it want's to stall sounds like an ICV issue, any vacuum leak would typically result in a high idle, not a stalling scenario.

[knick_knack]

Fuel rail doesn't need to be bled, any air just gets pushed through the return line.

Thanks, that's what I figured.

The fact that it want's to stall sounds like an ICV issue

But I can't maintain a low RPM (under 2000) even with throttle, which suggests to me that it isn't an ICV issue. Once I'm giving it any amount of throttle the ICV is no longer involved, right?

any vacuum leak would typically result in a high idle, not a stalling scenario.

I remember that forgetting to replace the oil cap or fully seat the dipstick led to stalling. And the Bentley, under "Starts But Will Not Keep Running", says "The second most common fault is caused by vacuum or air leaks."

[jlevie]

A systematic approach to diagnosing and fixing this can be found in http://www.r3vlimited.com/board/show...5&postcount=12

[Bullet Ride]

I remember that forgetting to replace the oil cap or fully seat the dipstick led to stalling. And the Bentley, under "Starts But Will Not Keep Running", says "The second most common fault is caused by vacuum or air leaks."

A small vacuum leak will typically cause a high idle and the car will run a bit lean. A large vacuum leak will cause the car to go so lean that it wants to stall out.

So since yours won't rev below 2k rpm, maybe it's a large vacuum leak. Did you remember the o-rings on the crankcase vent tube when you put the manifold back on?

[knick_knack]

Thanks, Jim, but that link doesn't work for me. Mind trying again?

Bullet - I did put the o-rings on, but I didn't have the washer under the spring on the bottom side of the tube. I just took everything off and put it back together with the washer, but there is no change.

I tried driving it just out of curiosity and it is misfiring and backfiring like crazy. Could that be explained by a vacuum leak? Or would that be better explained by something else (namely the AFM or TPS)?

[dnguyen1963]

Why a smoke test not the first troubleshooting tool for idle issues is beyond my comprehension!

[Kershaw]

Thanks, Jim, but that link doesn't work for me. Mind trying again?

Bullet - I did put the o-rings on, but I didn't have the washer under the spring on the bottom side of the tube. I just took everything off and put it back together with the washer, but there is no change.

I tried driving it just out of curiosity and it is misfiring and backfiring like crazy. Could that be explained by a vacuum leak? Or would that be better explained by something else (namely the AFM or TPS)?

http://www.r3vlimited.com/board/showpost.php?p=4472715&postcount=12

I think he was trying to link this post.

[Seawolf]

What year is your car ? Is it equipped with a C191 plug (round plug and socket under the intake manifold) and did you disturb it while working on the intake manifold ?

If so it may warrant some careful inspection and cleaning. That C191 plug feeds the injectors. While you're in there just check there's no fuel coming out of the FPR vacuum line.

Backfiring would lead me to suspect ignition or possibly ignition triggering e.g. CPS wiring/plug.

[knick_knack]

Thanks for finding that link, Kershaw.

Seawolf - it is a 1990 325is, so it does have the C191 plug. The misfiring makes me think that it is an ignition timing issue as well. What should I be looking for on the C191 plug and the CPS? Just clean all the connections I can find going into the C191 and try starting it again?

[e30topdown]

The CPS and induction sensor from the spark plug wires are connected correctly, right? You didn't leave one unplugged or they aren't backwards, are they? Not even sure if this is possible, but they do look a lot alike.

[knick_knack]

The C191 plug looks good from a visual inspection, as does the CPS (is this what the Bentley calls the reference sensor?).

Is there any easy way to check their signals at the ECU using a multimeter?

[hwy84]

Did you get this resolved?

If not, check to make sure your TPS, AFM, and ICV connectors are all on the appropriate sensor.

Did you possibly move the TPS on the throttle body by accident when you removed it or set it aside?

Seems like your DME doesn't know it's at idle, or can't keep a steady idle now that you haven't got a vacuum leak. Could your throttle stop have been adjusted incorrectly before the fix, in a misguided attempt to cure the idle issue, and now it's causing a no idle situation?