John Speake

The title of this thread and your subsequent comments in it make it clear you think the rebuilt MAF is responsible for the "problem". You are ignoring the fact that you had low intake manifold vacuum and a very high idle pot setting before the MAF change.

If you obtained your rebuild MAF from my agent Louie Ott, then please return the MAF to him for testing on his flow jig. If by mischance it is out of spec. then he will replace it FOC. If it is within spec. he may charge you for the service.

At least then you can then eliminate the MAF from your investigations.

Louie928

I've read your thread and I don't see why you think you have a MAF problem other than the CO pot value isn't within a suggested range of values. The CO pot is like an idle mixture adjust on a carburetor. You don't need any equipment to get an acceptable adjustment. Set it so the engine idles smoothly. You do have low intake vacuum at idle which is probably the root problem. Since you have checked everything else it could be cam timing or distributor timing. Are both distributors sync'ed correctly?

You can send me the MAF for checking. I charge $35 for testing which includes shipping back to you. I cannot test with the CO pot since that setting is engine specific. I can check for the specified MAF output voltage with a known air mass flow. If the basic MAF output is low, then that could affect your CO pot value.

I checked customers back since 2011 and I don't see where you bought the MAF directly from me, but I'll check it anyway.

Ott's Performance
2485 Dry Creek Rd.
Mosier, OR 97040

85euro928

John,
I didn't get the MAF rebuilt by Louie. I was going to have you do it but was afraid I wouldn't get it back in time for SITM so I had it rebuilt at another service. That said it's not the MAF as I installed a known good MAF last night with the same results. I apologize if I led you to believe you or anyone else that the rebuild was done by you; that wasn't my intention. I directed my comments to you as you are the resident expert in this area.

The reason I believed it was the rebuilt MAF was because the car ran fine, I took the MAF off, had it rebuilt, reinstalled it, and now the car runs like crap. It's was too coincidental to think it was anything else.

DKWalser

More than a little curious: Why would you have your MAF rebuilt if the car was running fine?

85euro928

Because in order to get the car to run fine I had to tune the MAF CO pot to over 900 ohms, which means the MAF is on it's way out.

Pfc. Parts

I understand the MAF rebuild (I almost sent mine to Louie last year for the same reason, but then discovered the root problem was a huge vacuum leak). What I'm not understanding is the low vacuum condition you report. That troubles me. Where could it be coming from? You said you ran a smoke test with no negatives. I don't get it.

Pfc. Parts

FWIW, here's where I found my problem. This was an 85 US intake and friction from manifold vibration wore through the hose.

85euro928

Tonight my plan is to pull intake center piece to install a new TPS, when I'm in there I'm going to take a closer look at all the hoses, if I don't find anything I'm going to do another smoke test but this time I'm going to do it using 8-10 psi.

85euro928

Update:
- I borrowed a better vacuum meter and read 19" of vacuum, better than 16 but still not to spec.
- I built a rig to pressurize the intake using a 3" PVC cap. I hooked my home-made smoke rig up to the intake and empty an entire cigar in to it, then I pressurized the intake to 4 psi, nothing, not one leak!
- I pulled the intake and replaced the TPS taking care to make sure I hear the switch when the throttle is released.
- Put everything back together, start her up, and it sounds pretty good, but still not perfect.
- I let it cool off and replace the Temp II. Start it again and in order to get it running smooth I need to keep the idle up around 850 rpms which makes the CO around 11 or 12 at 380 ohms.
- I turn the CO pot on the MAF CCW until I see a AFR of around 14, the car is running good. When I hit the throttle the AFR stays in the 13 to 14 range. I'll take it, at least it's running!
- While I have everything apart I decide to read the voltage across the Auxiliary Air Valve, I get 11.4V at the plug and 17.8 ohms at the valve.
- I leave for an hour and when I come back I decide to measure the MAF ohms at the LH plug as I had turned it quite a bit CCW to get the AFR up in the 14 range at idle. I get 186 ohms. A little low so I set it to 382 ohms and start the car. The car runs like crap again, as bad as it did when I first started! I'm also reading around 16 on the AFR and have to turn the idle to 1000 rpms just to keep the car running. When I hit the throttle the AFR jumps up to around 21, ugh! This is opposite of what is supposed to happen???
- Turning the CO pot CCW does very little to increase the AFR so I crank it all the way CW to get about 15 AFR.
- So I let the car idle as best it can to see what happens when it warms up. When it does, and the electric fan kicks in the AFR jumps from 15 up to around 18. And it does this every time the fan kicks in??? WTF!!!

Currently I'm taking a break and will start in again tomorrow.

Hilton

No, it doesn't. It means you had to adjust the idle mixture that far to make the car idle smoothly.

There are a number of reasons the car would be running so lean that you needed to adjust the potentiometer that far, including vacuum leaks, clogged/dirty injectors, fuel pressure/delivery problems etc.

Yes, an aged MAF will tend towards lean too, but its not the sole cause, and given the idle symptoms, I'd be looking elsewhere first.

Edit: Also, on S4's (and presumably LH2.2 ecu's too), CW makes it richer (increases the ohms on the pot), CCW makes it leaner. Make sure you're adjusting the mixture with the car fully warmed up however, as otherwise you'll find it drifts due to temperature compensation from Temp II input etc.

85euro928

Does any know if the Auxiliary Air Valve could cause a lean condition, or would it just cause a high idle? It seems to me that this is metered air so I doubt it would cause a lean AFR, however, I removed the AAV and popped it in the freezer for an hour and based on some photos and a video here on RL it opened fully. Then I put it in the oven on 210 degrees for an hour but it never fully closed, there was still a small slot that remained open. I'm not sure if this is normal or not or if it would even affect the idle.
BTW, I ran a pressure test of the intake again and with three of us listening with hoses to our ears I still didn't find a vacuum leak. I also slowly ran an open propane torch (off) over every hose and connection I could find, nothing. This leads me to believe that it's a fueling issue but since I can adjust the fuel pressure to 60 psi with the FPR and the fact that I can pinch off the fuel return line and get over 60 psi I'm thinking the pump is good. To me this leaves the injectors suspect.

Pfc. Parts

I can't comment on the air tests you've done and I use Dwayne's apparatus to check for vacuum leaks ( http://dwaynesgarage.norcal928.org/1...%20Refresh.htm ) but I can say the symptoms you're describing are similar to the ones I had after completing an intake refresh and I traced them to two bad injectors that weren't firing (stuck). Some folks think you can find the bad ones with a stethoscope but I ended up taking each of them back out and testing them on a bench with a 9V battery.

dfrhodes

so what happened when you swapped the LH out?

85euro928

Scott,
I used a similar apparatus to Dwayne's but used it along with a home-made smoke machine, three times. I'm confident there's no leaks in the intake.
My next steps are going to be to replace the fuel pump and send the injectors out for cleaning, and to look at fixing my adjustable fuel pressure regulator which is I found has a very slight vacuum leak. I'll report back when I get this all done.

85euro928

I got the same results, only worse. The LH and EZF that are in the car now have John Speakes chips in them that actually address the lean fueling issues with the euros so at idle I was down an one additional AFR.