This is a customers 2002 SSEi. The car will not idle on a cold start, you have to keep feathering the throttle and keep it above 2k RPM to keep it from dying. After a couple minutes, it will start running better and not require any feathering. It will idle fine while warm.

Customer already replace the MAF & IAC. I've tried switching back and forth between open and closed loop, no change. O2 values are right on target, jumping from 100-800mv. I reset the fuel trims, and noticed that the STFT is always resetting to 20%, not 0 like it should... unless under throttle. Fuel pressure is 45psi at idle while warm, and jumps to 50psi when removing the vacuum line from the FPR. To me, it seems like it would be fuel related, but where?

I could just throw some parts at it and replace the fuel pump, injectors and FPR, but I'd rather know what actually fixes it. Any ideas?

_________________
Andrew - owner/operator of Bonnevilles Unlimited

2004 Bonneville GXP | 60k | White Gold Tricoat | custom built supercharged 3800 hot rod | garage queen
1997 Corvette | 55k | Silver Metallic | Z06 wheels | Date-night Hauler/Parts runner
2014 Town & Country Limited | Cashmere Pearl | 95k | Family Hauler
2002 Ram 1500 Quad Cab Sport | Black| 260k | Official Bonneville Hauler

Maybe the O2 or computer are bad?

_________________

WHITE WHINE - 1992 SSE Supercharged 236.26 ci (.040 Over) 15.090 at 90.2 MPH on old engine w/ slipping trans & melted O2 sensor - Gen 3 M62 and matching TB, Gen 2 Pully, Zillamotorsports Ported LIM, YT 1.72 Roller Rockers, SII FPR & Injectors, Hypertech Thermomaster chip w/ 160 Thermo, TransGo Shift Kit, Infinity/Pioneer Speakers & a 10" Alpine Type R Sub, all the watts, 140 amp Alternator, Ricepipe CAI w/ heatshield, Pilot Angel Eye Foglights, Clear Corners, '02 17" Chrome Bent 5's, Magnaflow F-Body Muffler and Hi-flo Cat, Ceramic Coated Ported Exhaust Manifolds, Fan Override, Monroe Reflex struts, red calipers
2009 G8 GT - Sport Red Metallic, loaded, SOLO Axlebacks, Rotofab Intake, Tuned, autodim mirror, removed intake manifold cover, HSV GTS triple gauge pod, two tone red-hot shifter and HSV SuperSport steering wheel, GXP rear sway bar and diffuser, 3.45 diff and various Camaro suspension bits, LED Taillights

o2's are showing the correct values, so not sure about that. PCM is always a possibility.

_________________
Andrew - owner/operator of Bonnevilles Unlimited

2004 Bonneville GXP | 60k | White Gold Tricoat | custom built supercharged 3800 hot rod | garage queen
1997 Corvette | 55k | Silver Metallic | Z06 wheels | Date-night Hauler/Parts runner
2014 Town & Country Limited | Cashmere Pearl | 95k | Family Hauler
2002 Ram 1500 Quad Cab Sport | Black| 260k | Official Bonneville Hauler

Sounds very vacuum related. Either a cracked connection, maybe even a bad gasket?

_________________
Bye Bye:

RIP sandrock

Vacuum problem wouldn't go away when warm though. I've checked all the lines, they are good.

_________________
Andrew - owner/operator of Bonnevilles Unlimited

2004 Bonneville GXP | 60k | White Gold Tricoat | custom built supercharged 3800 hot rod | garage queen
1997 Corvette | 55k | Silver Metallic | Z06 wheels | Date-night Hauler/Parts runner
2014 Town & Country Limited | Cashmere Pearl | 95k | Family Hauler
2002 Ram 1500 Quad Cab Sport | Black| 260k | Official Bonneville Hauler

What about a grounding or electrical issue , metal expands when warm albeit slightly.

_________________

EGR maybe too.

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Boost addict


The Fleet:
'93 SSEi - Twincharged + manual Build thread
'97 Camaro - Top swap
'05 STS - V8, AWD, her DD
'92 Trofeo - Fair weather DD
'99 Montana - top swap 3800
'04 Sierra 2500HD - LLY Duramax

Current project:
Something cool, trust me.

Upcoming projects:
'92 Bonneville SSE
'87 LeSabre T-type
'67 LeSabre

Gone to greener pastures:
'84 Sierra Classic - Twin turbo 3800
'97 LeSabre - Top swap

RIP:
'86 LeSabre - pictures
'93 SE - L67

I would try an OEM MAF (we know how the reman'd ones are), I second the EGR.

Ding ding ding, we have a winner!

It was a brand new aftermarket MAF, and I had too much faith in it. Put a good working OEM one on it and it runs great. Seems like I always get stumped on the easy stuff because I over-think it.

_________________
Andrew - owner/operator of Bonnevilles Unlimited

2004 Bonneville GXP | 60k | White Gold Tricoat | custom built supercharged 3800 hot rod | garage queen
1997 Corvette | 55k | Silver Metallic | Z06 wheels | Date-night Hauler/Parts runner
2014 Town & Country Limited | Cashmere Pearl | 95k | Family Hauler
2002 Ram 1500 Quad Cab Sport | Black| 260k | Official Bonneville Hauler

Wondering if we should try resetting PCM after changing MAF to non-OEM sensor???
PCMs seem to love OEM, either new or used....

Perhaps a reset would force PCM to scan for and accept another type.

Just a thought.

MW

Turns out the MAF was a misdiagnosis. It seems to run better, but then the next day it was crappy again. I started throwing parts at it based off the incorrect STFT readings. I replaced the fuel rail/injectors/FPR. I had the car in the shop for 2 days, and it started perfect every time. I never took it out on the road though. Having then claimed "fixed" again, I parked it outside waiting for the owner to pick it up. The next morning I went to move it, and it started doing it again! I was pretty frustrated by this point, so I had one of my mechanic friends take a look at it. It had been sitting outside for 2 days at this point and when he went to start it, he could barely even get it running. He said the exhaust smelled wrong. He suspected either a plugged cat or bad gas. After that, I got in the car and was going to drive it across the street to my shop and I couldn't even get it running at all anymore. It had progressively gotten worse over the week. We towed it to my shop, and I drained the fuel tank. I put in 6 gallons of fresh 91 fuel. When I tried to start it, it still wouldn't fire. I pulled all the plugs and they were soaked in fuel. I put in 6 new plugs, and the first time I hit the key it fired right up, no hesitation at all. I took it out on the highway and it pulls hard just like it should. Correct diagnosis: bad fuel, probably water in it.

_________________
Andrew - owner/operator of Bonnevilles Unlimited

2004 Bonneville GXP | 60k | White Gold Tricoat | custom built supercharged 3800 hot rod | garage queen
1997 Corvette | 55k | Silver Metallic | Z06 wheels | Date-night Hauler/Parts runner
2014 Town & Country Limited | Cashmere Pearl | 95k | Family Hauler
2002 Ram 1500 Quad Cab Sport | Black| 260k | Official Bonneville Hauler

Wow! What a bear!!!

Glad you finally unravelled that mystery...Adding a bottle of HEET to my shopping list, just in case.