HP Junkies: Help with low idle issue.

[WydRyd]

Having a problem with my car where it's idling really low (300 RPM's) and stalls. Also runs very rough and lacking power. If I blip the throttle very quickly, I can hear light backfiring/popping.

I also have, what seems to be, a loose alternator belt because when I blip the throttle, I can hear it squeak. That needs to be tightened up I guess.

I checked all vacuum connections and all seem secure.

I removed all plugs and they were all heavily sooted with carbon deposits, so I replaced them with el-cheapo NGK's. That made no difference. I also checked and cleaned out the distributor and rotor. No difference.

Whilst idling (barely), I sprayed some WD40 where the inlet manifold meets the heads, to see if it made any difference to the idle and it didn't. Tried this with all 6 runners to no avail.

I have twin plugged heads, but my lower set of plugs are not connected yet. I'm only running single plug. I thought *maybe* one or two of the lower plugs fell out and has left a hole(s) in my heads, but they all seem secure and tight

I'm not sure what else to check/test. Getting real annoyed and worried.

I'm running 0.5mm C2 Turbo head gaskets, so I'm hoping one or two haven't blown out. Unlikely, but a possibility I guess.

I don't have a compression tester to verify cylinder sealing

Could it be weak ignition/bad alternator?

Any ideas/suggestions?

[dean]

It sounds like it is running lean. Did you change anything? Is your fuel filter old? Does it run good around town? Do you have an air/fuel meter? They are real spiffy to help diagnos problems.

Dean

[WydRyd]

The only thing I changed recently is replaced the OEM Carrera rubber boot (that interfaces the AFM to the Throttle Body) with a Nitrile elbow and tapped the AFM with a NPT fitting for the vacuum line to the ICV.

Fuel filtyer must be old, because I've never replaced it since I've owned the car for 4 years

Before it started idling low and stalling, it was running pretty crap. Hesitating and bucking and popping at part throttle

I don't have a A/F meter hooked up as yet. May have to hook it up asap to see what the heck is going on. I'm confused!

It would take a tonne of boost to blow out a metal C2T head gasket, so it's unlikely it's that!

[YermanCars]

Maybe your AFM is going, also check all conections by the afm, I can't what to get rid of that damn thing.

[YermanCars]

Check your rubber boot, I had the Same problem, either the afm or rubber elbow.

[WydRyd]

Souk, I replaced the rubber boot a couple months ago, with a Nitrile/Silicone one. The rubber boot was torn, so it was replaced.

Might rip off the AFM and silicone elbow anyway and double check it all

[MotoSook]

We had a low idle with Tony's engine, but it was not that low, maybe 700 RPM which I attribute to chip tuning as our chip is not the usual Stage 3 chip. It still idled well. On fast engine decel it might stall, but it was not bothersome prior to letting Tony drive off with it. We haven't put the finishing touches on it, but it may have something to do with a lower than normal manifold pressure at idle due to the plumbing.

I don't think your problem is what we experienced with Tony's engine. But try this: Disconnect the ICV connection at the AFM and plug the AFM port that you installed. Let the ICV breath at atmosphere while idling. Does did the idle increase? It's not a permenant fix, but it's one step toward a solution.

[YermanCars]

I will stick to cooking, and leave porsche problem solving to Souk.

I was leaning more toward the ruff running on exel, and when the afm blew up on me.

[MotoSook]

LOL...I'll have design a product to prevent AFM's from blowing their lids!

Edit: I just re-read Merv's first post and see that he's got driveability issues too. The Chef may be on to something. The high boost pressure might have done something to the AFM. Do you have another one handy Merv?

[WydRyd]

No, no spare AFM's unfortunately

How can I verify it is not a cylinder -> head gasket? Wouldn't it be smoking a lot if it were?

Could it be pulled head stud(s)? I'm using ARP hardware though

What about bent or sticky valves? Am I stressing too much? LOL!

It does smell overly rich at idle too. Could it be stuffed injectors?

[MotoSook]

Merv, you need to start eliminating potential defects/problems.

I usable compression tester is not very expensive (maybe 35 bucks in US).

Your rich condition makes me wonder if the 951 injectors have been overworked and are stuck open. Have you consulted Todd?

Any poofing noises above idle to indicate a blown gasket?

[WydRyd]

Yeh I consulted Todd and he suspects a vacuum leak too. HE was the one who told me it's possible that I've got a blown out head gasket, but to do that, one would have had to run a tonne of boost I've limited my boost to 1.1-1.15bar because my clutch cannot handle 1.25bar right now. Even then, Todd has run C2T head gaskets in these setups up to 1.4bar without a problem, so ???

He said to check inlet manifold gaskets, and I tried that by spraying WD40 around the runners with no improvement. Might be worth removing the whole intake anyway just to be sure I guess

I checked my CHT last night and it's OK too (measured 2.8Kohms to ground), even though it's a one wire unit. Should I just replace this with a two wire unit anyway, or leave it?

So far, spark plugs OK. Distributor cap OK. CHT checked OK.

I guess other things I can re-check:

- all vacuum connections/pipes before the throttle body.
- ignition coil? How do I test this?
- fuel filter?
- injectors?
- headgaskets? What visible signs would there be if there was a blown out head gasket???

[911Velocity]

Two thoughts, check for exhaust leaks all the way back to the muffler and after you have done what everyone else said to check try installing a set of correct heat range denso-iridium spark plugs as this made a world of difference when I was having trouble with backfiring and breaking up at 4000+ rpm. Car has run awsome since the change and I went through 3 brand new sets of bosch (west german made not US) plugs that did not help. Good luck.

Best regards,

[WydRyd]

Thanks. I just installed new NGK B8ES plugs, gapped to 0.6mm because the old plugs were HEAVILY sooted with carbon deposits. Made no difference.

I wondered why the plugs were that heavily sooted. Must be a over rich mixture I guess.

Would a vacuum leak not cause the engine to run lean, due to unmetered air entering the combustion chamber? I've never had an O2 sensor hooked up for years, so the ECU would not be receiving an A/F reading, and NOT injecting more fuel as a result of a lean mixture.

Could well be the 951 injectors