Hey folks!

I've had a progressing issue with my 2001 for quite a while. It's always during start-up but once running seems to run just fine. It seems to happen most when the car has been run up to temp, shut down for 30 minutes to an hour and when you come back, it's hard to start. Occasionally though, it has happened during a cold start.

What happened at first was it would crank excessively before starting. At least 5 seconds worth of cranking or more before it fired. Once running, it was fine.

As time went on it turned into starting for literally 1 second and then stalling immediately as if the key were removed. I can often keep it running by feathering the pedal. If I didn't feather the pedal I could probably have this happen 3-5 times in a row before it started. Again, once running it seems to run fine. Sometimes it'll also just start rough if it's able to start without stalling. It'll start, gently surge a few times and even out and stay running. I caught one of the rough starts on video which is linked at the bottom. I'm going to try and grab one of the start/stall.

I've done some testing of various components and can't really find fault yet. Fuel pressure is 48PSI, flips to 52/53PSI when throttle is flipped and returns to 48. FPR hose is dry and I even hooked it to a hand-held vac. pump to verify it holds pressure. Throttle body is spotless. MAP/MAF/TPS/IAT/CTS values look just fine when I read the PIDs with the scanner.

A few things that may be of note is I believe it is idling slightly low, usually 640/650rpm in gear foot on brake. I thought I remember it being exactly 750rpm some time ago. Also my MAP reading is 9.4/9.6inhg @ 650RPM. Not sure if that is "correct" or not. The car has 150K miles and the ICM and coils are originals so I have sort of been leaning towards the ICM but seeing as it's an expensive part to replace I'd like to be more sure. I've only measured the coil primaries and got the following values: 5.45/5.45/5.38 = 6/3-2/5-4/1 I still have to check the secondaries and OHM out the injectors. There are no codes by the way. I suppose I can take the ICM to the parts store also. Any suggestions in the meantime though?

Much appreciated!

The video of the rough start is here you can hear it if you turn the volume up, it's 30mbs though: http://www.reesebroody.com/bonneville/roughstart.mp4

I'd suggest starting with cleaning the idle air control valve, and the passages in the throttle body.

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*Gone, but not forgotten* - Black 2000 SSEi, HIR Headlights, Angel Eyes fogs, 3rd brake light overlay, hi-flo cat, 180 degree thermostat, HS 1.9 rockers, LSx yellow springs, Intense FWI, PCM, shift kit, push rods, and 3.4 Pulley. ZZP Power Log.

EGR maybe

When you're in the throttle body checking and cleaning the sensors, see if the blade itself needs cleaning as well.

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-Car Guy Carl
"Penelope" - 2003 SLE - 247k Miles
"Sydney" - 2000 Honda S2000 - 98k miles

Speaking of IAC I think I'm going to go ahead and replace that. It is original and new replacements aren't too expensive. These symptoms can certainly match a malfunctioning IAC valve. I had cleaned the TB closer to when I had noticed the very first symptoms of this. Took it off, removed sensors and cleaned it spotless. It still "is" spotless today, shoot all the small bypass holes at the bottom are all still clear. Cleaning it made little if any difference.

Here's a video of the start/stall I caught though. I feathered the pedal the third time to keep it running.
Start/Stall Video

I'll admit, first off, that I am really inexperienced, but I had the same exact thing happen to me on my '05 Bonnie. What I did on mine was 1) Replace all three ignition coils 2) Replace all 6 plugs and wires (I made sure to use the ACDelco Iridium plugs). Ever since then, it has not acted up *knock on wood*.

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2005 Pontiac Bonneville SE

That's certainly a possibility also. The ICM is an expensive piece though, coils aren't too bad. All original on my car with the exception of the wires and plugs which have been changed before. ACD Iridiums in now. Have had two instances so far where the engine idle was very high ~1500-2000RPMs and wouldn't come down. Had to shut the car off and restart a second later and each time it started high for a second and came right back to "normal" on the restart. I haven't ordered the IAC valve yet but the more I see the more it points to that. We shall see. Thanks for the input!

I just wanted to reply back and say the IAC made absolutely no difference. Issue still remains.

I had the exact same problem, but I was getting transient error codes for the TPS, IAC and O2 Sensor. The cause was un-metered air entering through the throttle body. Took a different Throttle body to fix it. Just thought I should throw that in there. If no one mentioned it, might be a Cam Shaft Position sensor too. - BC

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In Memory of Brad - 1/21/1977 .. 10/23/2013 ...... Aaron - 1977 .. 2017 .....
2017 Hyundai Santa Fe Sport ..... 1992 Bonneville SSE 1SB 170 HP L27 4T60E retired/sold to MattStrike ..... 2005 Bonneville SE 1SC 205 HP L36 4T65E - retired/salvage yard ..... PBCF user 2321