Rough Idle & Low /Unstable RPMs
 

2002 4.6is - Supercharged - 109k

What's been done:

Rebuilt Supercharger due to blow-by; oil going into the throttle body/intake

Sprayed 2 full cans SeaFoam (different times) into intake. Result: Driver (LHD) side blows out lots of smoke after, clears up.

Both Cats removed trying to chase the issue.

Pulled plugs on bank 2, inspected, cleaned and replaced.

MAF has been cleaned as well as air filter.

New coils.
__________________________________________________ __

Code: 20 | Lambda code probe 2 rear cat | may be bad wire

When I view it in INPA it says running rough, but if RPMs are increased by 100-200 it goes to 100% clear/perfect.

Running low on ideas. Was thinking MAF maybe, but its not tossing a code. If I unplug the MAF it cuts off - meaning its a good part.

Possible throttle body issue?

Thanks for any suggestions!

Does it settle down if you spray starter fluid in the intake? Caution here!!!
Had 3 bad injectors on a motor once and an independent shop used this method to determine a fuel issue. I'd also check fuel pressure to be sure there was enough and not fluctuating.

Rough Idle & Low /Unstable RPMs
 

Idle control valve if idle sucks and you can make it run nice manually. MAF is very indeterminate but if you unplug and conditions improve it's likely the fault.

Car should run without maf but not sure if you unplug while running what happenes or if engine is warm already.

Because it's supercharged it doesn't behave well when you pull duct work off. I've not had a second person on hand to keep it running with spraying it in the intake with the engine running.

I will source a gauge and check the fuel pressure. Im sure it's due for a fuel filter as well.

Where is the idle control valve? Is on on the TB unit? I can make it run manually by gently hitting the gas ever so slightly. I did this while running inpa in real-time and all the cylinders run perfect.

Update: with engine at operating temp, it shuts off immediately if MAF unplugged.

Pretty sure MAF is faulty. somebody on the forum recently did this same test. Borrowed MAF from wife's car (had to apollo 13 the thing in there with duct tape) same exact happened. When cold the car uses lookup tables to meter air fuel mix. When warm relies on MAF and O2.

You can look at live reading on MAF or even back probe and measure the voltage for some common sense values to confirm.

Just use tire pressure gauge. Also: not likely on fuel filter. They are "lifetime" filters and can last half a million miles. The pressure regulator can fail though.

I'n the 100s of threads I've read on fuel system I've never seen a case of fuel filter being a problem source. Since it's combined with the regulator sometimes that part needs to be replaced but the filter is maybe 100-200x the size of the tiny filters of olde that needed periodic replacement.

Sprayed starter fluid all around the intake, throttle body etc - no evidence of RPM change.

Have not checked fuel pressure yet. Continually running seafoam in the tank. It came from Montana and had a lot of dusty dirty in all the fun places.

Have you done a compression test on all cylinders to determine the health of the engine. A misfiring cylinder will smooth out and be masked if you run the rpm high enough. Low compression in one cylinder could be the cause of the problem and racing the engine just mask the problem.