Hopefully some of the geniuses on the boards here can offer their input on this….
I’ve got an 04 STi w/~135k miles, owned since new (July 2003) and Cobb Stage II with a GodSpeed pro tune since 40k miles. A couple of weeks ago I was out running errands, about to prep my 04 STi for winter storage with a dose of Sea Foam and a fresh oil change, as I do every year. The car was running normally, smooth as ever, and driving / idling normally with no issues.
I made a stop for about 10-15 minutes, 1/4-tank of gas (pre-Sea Foam), and then when I started the car, suddenly it wouldn’t idle. Feathering the gas keeps it running, and driving around it runs smoothly and pulls strongly with no apparent misfires until I let it idle, when the engine again tries to quit. Adding Sea Foam and filling the gas tank made no difference in behavior, even after ~15 miles of driving.
Highway driving doesn’t trip a code, but the misfiring at idle does. The dealer checked and found a code for a cam timing issue, but after clearing the codes it didn’t come back. Diagnostics showed misfiring on cylinders 1, 2, and 3.
Inspection of the timing belt showed that cam timing was spot-on, and the belt (replaced @ ~95,000 miles) was in great shape. Spark plugs look normal.
I had a similar behavior 3 years ago, when on a cross-country road trip the fuel pump and sending unit went out; the car would run great for hundreds of miles at a stretch, but wanted to die anytime I stopped for fuel and let the RPMs fall. Sending unit and pump got replaced at the time and the problem.
For my current issue, the dealer mechanic ran a compression test, and while they’re below 140 (averaging around 130), all are within 10% of each other. Dealer wants to rebuild the valve train (to the tune of $3k-4k) to eliminate carbon deposits as a cause.
In my mind - however off-base - it seems to me that if carbon buildup on the valves was the cause, it wouldn’t be a sudden-onset, acute idling issue; it would have developed gradually over time. In my case, it was like someone flipped a switch in the midst of my errands, with no backfires or incidents to disrupt the engine, just tame around-town driving.
Does anyone have any suggestions for a troubleshooting approach that might be fruitful, and cost less than a valve train?
I’ve got an 04 STi w/~135k miles, owned since new (July 2003) and Cobb Stage II with a GodSpeed pro tune since 40k miles. A couple of weeks ago I was out running errands, about to prep my 04 STi for winter storage with a dose of Sea Foam and a fresh oil change, as I do every year. The car was running normally, smooth as ever, and driving / idling normally with no issues.
I made a stop for about 10-15 minutes, 1/4-tank of gas (pre-Sea Foam), and then when I started the car, suddenly it wouldn’t idle. Feathering the gas keeps it running, and driving around it runs smoothly and pulls strongly with no apparent misfires until I let it idle, when the engine again tries to quit. Adding Sea Foam and filling the gas tank made no difference in behavior, even after ~15 miles of driving.
Highway driving doesn’t trip a code, but the misfiring at idle does. The dealer checked and found a code for a cam timing issue, but after clearing the codes it didn’t come back. Diagnostics showed misfiring on cylinders 1, 2, and 3.
Inspection of the timing belt showed that cam timing was spot-on, and the belt (replaced @ ~95,000 miles) was in great shape. Spark plugs look normal.
I had a similar behavior 3 years ago, when on a cross-country road trip the fuel pump and sending unit went out; the car would run great for hundreds of miles at a stretch, but wanted to die anytime I stopped for fuel and let the RPMs fall. Sending unit and pump got replaced at the time and the problem.
For my current issue, the dealer mechanic ran a compression test, and while they’re below 140 (averaging around 130), all are within 10% of each other. Dealer wants to rebuild the valve train (to the tune of $3k-4k) to eliminate carbon deposits as a cause.
In my mind - however off-base - it seems to me that if carbon buildup on the valves was the cause, it wouldn’t be a sudden-onset, acute idling issue; it would have developed gradually over time. In my case, it was like someone flipped a switch in the midst of my errands, with no backfires or incidents to disrupt the engine, just tame around-town driving.
Does anyone have any suggestions for a troubleshooting approach that might be fruitful, and cost less than a valve train?