Due to an incident totally my e30 in 2020 I transferred all useable components to a new chassis. Car drove great before, the impact was at 70mph where the car blew a rear left tire and sent me sideways into a ditch, I walked away completely fine so id like to think the motor did too 🤞🏾 but it did break the weld on the motor mounting on the subframe. It's been a year now and ever since ive been having an erratic idle and possibly may be getting worse slightly. Ive been slowly trying to track it down while solving other pressing issues that came with this full year on build. Most wear items on this car is new aside from major components.
Symptoms
- The car drives great never stumbles on acceleration, ever.
- Once driven, mostly on a highway then coming to a offramp stop the idle often times will sit high above 1k and slowly come back down to regular idle. This fluctuation happens at times randomly but not as much on cold star.
- The best way to describe the idle is a slight steady bucking
- When you put your hand near the tail pipe the exhaust puffs out and is in sync with the engine bucking, this puffing stops when you rev the engine.
- A new one that occurred in the last month, it's stalled 2 times while cruising downhill coming towards a stop, very very odd and im not too sure what clue thats adding to the issue.
- Check engine comes once engine warms up, goes away under load and returns on at idle after 5-10 secs
- Borescope cylinders look great, spark plugs dont show signs of a misfire, great wear after 13k miles.
- I had a fat exhaust leak which I though was the issue, supersprint headers, stock cat and supersprint exhaust, I sent it to a shop to delete the cats and put a mid section in, leak fixed but not the idle
Since January slowly ive replaced:
Cap/rotor
spark plugs
Ignition wires
injectors
Fuel pumps (wallbro upgrade - 2nd pump was replaced and is still inline)
CPS 6 years old
Valve Cover gasket and 4 rubber rocker rod plugs
Oil Cap
swapped 02 sensor
swapped MAF
swapped Idle control valve (the one I swapped with caused it to idle even more oddly, maybe this one isn't programed for a m20b25 or maybe its the problem, I should probably also try running the car with it unplugged)
Yesterday I did a leak down test and compression finally, everything came back great 160psi across the board on Compression with very low loss on the leak down. Ive also performed a vacuums leak smoke test twice, im not seeing any leaks but id also like to do this indoors. Ive also sprayed starter fluid near every vacuum component, no luck.
Things left im going to look at replacing:
brake vacuum check valve
I would replace the brake booster but they seem to be discontinued... could very well be the problem as I did have some occasional braking issues.
Fuel pressure test (is there a such thing as too much to the regulator?)
Any other ideas based on my symptoms is veery appreciated, im pointing towards vacuum leak but would it cause that kind of bucking idle?? Video of idling below.
End of the video is probably the best, may do one under the hood if needed
Symptoms
- The car drives great never stumbles on acceleration, ever.
- Once driven, mostly on a highway then coming to a offramp stop the idle often times will sit high above 1k and slowly come back down to regular idle. This fluctuation happens at times randomly but not as much on cold star.
- The best way to describe the idle is a slight steady bucking
- When you put your hand near the tail pipe the exhaust puffs out and is in sync with the engine bucking, this puffing stops when you rev the engine.
- A new one that occurred in the last month, it's stalled 2 times while cruising downhill coming towards a stop, very very odd and im not too sure what clue thats adding to the issue.
- Check engine comes once engine warms up, goes away under load and returns on at idle after 5-10 secs
- Borescope cylinders look great, spark plugs dont show signs of a misfire, great wear after 13k miles.
- I had a fat exhaust leak which I though was the issue, supersprint headers, stock cat and supersprint exhaust, I sent it to a shop to delete the cats and put a mid section in, leak fixed but not the idle
Since January slowly ive replaced:
Cap/rotor
spark plugs
Ignition wires
injectors
Fuel pumps (wallbro upgrade - 2nd pump was replaced and is still inline)
CPS 6 years old
Valve Cover gasket and 4 rubber rocker rod plugs
Oil Cap
swapped 02 sensor
swapped MAF
swapped Idle control valve (the one I swapped with caused it to idle even more oddly, maybe this one isn't programed for a m20b25 or maybe its the problem, I should probably also try running the car with it unplugged)
Yesterday I did a leak down test and compression finally, everything came back great 160psi across the board on Compression with very low loss on the leak down. Ive also performed a vacuums leak smoke test twice, im not seeing any leaks but id also like to do this indoors. Ive also sprayed starter fluid near every vacuum component, no luck.
Things left im going to look at replacing:
brake vacuum check valve
I would replace the brake booster but they seem to be discontinued... could very well be the problem as I did have some occasional braking issues.
Fuel pressure test (is there a such thing as too much to the regulator?)
Any other ideas based on my symptoms is veery appreciated, im pointing towards vacuum leak but would it cause that kind of bucking idle?? Video of idling below.
End of the video is probably the best, may do one under the hood if needed
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