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Ok please i need help i have a 1997 318i bmw convert 5 speed with a 1.9 m42 motor. I have checked cleaned and rechecked everything and still the car has a rough idle and when accelerating out of 1st gear and every gear after the motor cutss out boggs down and has ZERO power but car doesnt stall when i take foot off pedal power comes back. Also when idling n neutral no problem u can rev it all the way to redline with no bogging out but as sonn as u put in gear and start driving it starts cutting out and even once i finally get up to speed still keeps cutting out when i press gas. Its like the gas and spark get cut from car Only engine code i get is po120 which is tps a circuit malfunction.
I have changed and checked the following:
Tps switch twice
Icv
Maf cleaned
Cam sensor
Crank sensor
Checked for vacuum leaks found none
Cleaned throttle body
Plugs
Air filter
Checked all wiring harness connections
Changed out charcoal cannister/vapor regulator
Stumped frustrated and confused, what else am i missing? Im gonna change fuel filter tomorrow but didnt think that was issue since it revs up fine with no issues while sitting, idle is wierd though it will be rough and u touch throttle cable and it clears up u rev it once and it goes right back to rough idle.
Please help
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Replies
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Misses under load are often ignition related. I know you say you changed the plugs but you might want to check for voltage leaks. You might also check for vacuum leaks as they are also another common source of a problem like that. I’m going to post some videos that might help you figure this out.
Vacuum leaks
http://www.youtube.com/watch?v=9CPqbaSgcok+
Voltage leaks
Power Balance
Solving Performance Problems 1
Solving Performance Problems 2
Re Performance Problems
thanks eric for the info and vids, here’s an update on the bmw. Today I replaced the fuel filter and did your voltage leak test and found nothing arcing, I also forgot to mention the spark plugs wires are less than year old. I also removed the entire upper manifold and rechecked ALL the hoses and seals on the throttle body and breather canister/maf system…AGAIN. I had already did the carb cleaner trick to check for leaks and did it again today but found none. Still the car boggs down and idles rough, I have a question bout MAF I cleaned it with carb cleaner do you think I might have damaged it? I know in your video you say you use carb cleaner and when the car is running I disconnect the MAF electric plug and car gets worst. The only time I throw a MAF code is when I intentionally unplu while car is running. I dont want to have to buy a MAF if not needed its over $300 with no return policy, but don’t know if my is working or not or just registering via electric plug but not regulating air flow from possible damage from cleaning? Still stumped on what the problem is, and last the TPS code po120 I have replaced the tps twice and still keep getting code checked wire connection and it has power and when unplug that connection from tps while car is running nothing changes?
This problem is a little beyond my skill set but I would start with the simple things first. When the new plug wires were installed, are you certain the wires were replaced in the correct order? I would double check spark plug wire routing — that would be a goofy problem that could be fixed easily. This sounds like either a problem with spark timing or maybe a compression problem. Does it have a timing belt, and when was the belt last changed? A power balance test and a compression test would be reasonable. It might be very useful to examine this vehicle with a labscope to be sure spark timing is correct. Failing those possibilities I would wonder if the cat could be obstructed…. At this point I would be heavy on the investigations and light on replacing any more parts.
When you replaced the TPS did you set it to spec? They need to be adjusted for proper voltage readings when you install new ones. Usually between 0-.5v closed throttle, 4.5-5v WOT. If it’s not adjusted correctly then it may cause the condition you have. Also it’s VERY important that you don’t have any air leaks in the tube that runs form the MAF sensor to the engine, any holes here can really offset the fuel mixture so be sure to fix those should you run into them. It’s also not a bad idea to make sure you have the proper signals at the TPS wires, if there’s a wiring problem disrupting the TPS signal it could cause the same issues as a bad TPS.
As for an exhaust restriction you can check for this by removing the O2 sensor and taking it for a drive, if the performance issue goes away or changes you may have a restricted exhaust which would require further investigation.
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