'98 V70 Turbo - swapped a complete subframe engine/trans FWD into AWD. Implant was known functional engine/drivetrain.

The engine swap is complete and it took a while before I had fuel in the injectors to get it started. But it did not idle. At all. I could keep it running by feathering the pedal.

I swapped the ECU and TCU thinking it had something to do with FWD and AWD units. But I don't think there is a difference - at least w/ '98 70 series.

I found an injector connector no fully seated, but seating it gave no improvement.

I looked for vacuum leaks and found none. It idled like it had a massive one.

I swapped and cleaned a MAF with no improvement.

Finally I simply disconnected the MAF. Now it idles, a little rough, and with an occasional pop (detonation?) coming from the intake.

I have another MAF I can swap in, but would appreciate any answers to these questions:

1) What causes detonation in the intake manifold?

2) Why would it idle better w/o MAF than with it? (Is the idle control valve that good at its job? At the least I know it works well!)

 

I've spent a few hours looking, fiddling, thinking.

The super crappy idle really seems like a huge vacuum leak. So I checked all the vacuum lines. There aren't that many. I found one with a marginal seal and put a clamp on it. I found a small line disconnected. Neither made a difference.

It was also seemed hard to believe I had 2 MAFs bad from 2 previously running (well) cars.

Furthermore, when I put it in gear and moved back/forth in the driveway, the brakes barely worked...because there was no vacuum!

So I turned my attention to the intake manifold. I found a few bolts not as tight as I like. The detonation in the intake stopped. The idle wasn't much improved, but the brakes were now getting some vacuum.

Tomorrow I will remove the intake manifold and reseal the gasket. I really think (and hope) that is my problem!

 

Cause of problem discovered and remedied. In a moment of careless/thoughtless (not sure which) work, I caught the sheet metal bracket between the manifold and the head. The bracket should be on the outside.

So I'm relieved I found the root cause, but confess some embarassment at my gaff.

Now the car runs awesome! I look forward to a longer ride when I can get into the boost a little.