Mondial Backfire & Idle Problems

Sounds like maybe a bad Digiplex ground..

 

Possible fuse box problem. Do search on fuse boxes there's plenty to read. Your next parts order might be with Birdman. Good luck and keep us posted.

 

If your tach dies and you lose an entire bank, it is a flywheel sensor. Mine went bad but it started out like your car.

 

The guys above already mentioned some of the common causes, and you checked the extenders, so I'll add the coil/plug wires themselves (how old are they?), the connectors between the digiplexes and the coils, vacuum leak, and contaminated fuel. Much less commonly a coil.

definitely not the idle speed or throttle position setting...that's just somewhat masking the problem.

probably the easiest thing to do is get a timing light or those cheap in-line spark testers and check the spark on each cylinder and on the coil wire.

if the problem is on one bank, yank the coil secondary wire from the coil and check for corrosion. Also check the primary wires for loose fit or corrosion.

Then search for how to test the flywheel sensor for that bank (best to do it from the digiplex connector so you also check the other connectors in the circuit).

testing the coil can be done by swapping the coils. Pay attention to the wire colors.

if the problem is intermittent on both banks, the digiplex grounds are a good bet.

disclaimer: the above applies to the 308 only. The 328 has a single ecu, one flywheel TDC sensor and electronic modules on top of the coils. The primary ignition testing procedures and common failures are different.

 

It sounds like a vacuum leak.

Birdman

 

My Mondi was doing the same sort of thing, though not as bad. It would only settle down to 2K idle at a light. If I used the clutch to slow the engine to 1,000 RPM, it would stay there until I blipped the throttle, then settle at 2,000 again. I never did definitively identify the problem. I replaced vacuum hoses, lubed the VLV and put it back together. Problem was gone. So it WAS a vacuum leak somewhere. I can only suggest that you poke around, look for something unhooked or a ratty looking hose. These things have a bunch of vacuum hoses and any one of them could cause it.

If you have disabled the fast idle, make sure none of those hoses have an open end.

I also had a couple years ago a bad crank sensor which was causing the car to malfunction, but not backfire. It would stumble, or lose power, then come back. I didn't figure it out until another fchatter riding in the car noticed that the tach went nuts when it happened. I looked at the schematic and saw that the tach was driven off only one of the digiplexes which showed that it was the crank sensor on that digiplex.

Birdman

 

Vacuum leak. Also check your extenders and spark plug wires to make sure everything is snug.