E30 Misfire at Operating Temp HELP

**cole45acp** · 11-19-2022, 10:17 PM

Hey guys, my '85 eta has always had a misfire problem, though recently (as of today) it has gotten much worse. I used to be able to drive the car for about an hour before it would start to sputter and lose power every time I accelerated hard after 2500-3000 revs. Though today, the problem seems to have gotten much worse and occur sooner. Keep in mind that the car only starts to misfire WHEN THE CAR IS AT OPERATING TEMP ONLY. When I cold start the car, it pulls hard and there are no issues, sputters, or loss of power. Once it's warmed up is when this problem starts to occur. IT DOES NOT MISFIRE IN IDLE EVER, ONLY WHEN ACCELERATING. Things that have been replaced since I've owned the car include, Valve Cover Gasket, Inline Fuel Pump and Filter, Spark Plugs and Wire Set, Ignition Coil, Distributor Cap and Rotor, Throttle Position Sensor, All temp sensors and thermo-time switch. I purchased the car a year ago and it has an aftermarket exhaust installed with no o2 sensor. Could no o2 reading be causing this issue? I'm unsure, and advice you guys have would be great thanks!

**82eye** · 11-20-2022, 12:59 PM

missing 02 sensor means the ecu isn't getting all the info it needs. definitely can cause bucking, bogging, surging issues. the ecu uses the signal to adjust air/fuel mixture.
without the signal it will go to a set fuel map that will only work so long depending on conditions, it may also default to a limp mode.

**cole45acp** · 11-20-2022, 03:15 PM

Okay interesting, I experience all of the symptoms you've mentioned on a daily basis with the car. I'm getting a new aftermarket exhaust made for the car within a couple of weeks. Assuming I can just take the shop a new o2 sensor and they'll know what to do? (threading it into the pipe where it needs to go this and that?)

**82eye** · 11-20-2022, 07:13 PM

Originally Posted by cole45acp

Okay interesting, I experience all of the symptoms you've mentioned on a daily basis with the car. I'm getting a new aftermarket exhaust made for the car within a couple of weeks. Assuming I can just take the shop a new o2 sensor and they'll know what to do? (threading it into the pipe where it needs to go this and that?)

i'd let the shop you need one installed. they'll need to install a bung if there isn't one.

**cole45acp** · 11-26-2022, 01:40 AM

Okay, just odd that the car ran fine for over a year without the o2 sensor plugged into anything. Why would it be a problem now? ECU finally was like hey somethings going on here?

**323i E30** · 11-26-2022, 04:56 AM

That is weird indeed.
Doesn’t the ecu ignore the sensors until it’s at operating temp? Did this start happening after replacing the temp sensor by any chance..?

Could be I’m wandering off a bit here, but maybe you have a big intake leak, which is no problem when the engine is cold and running rich as it does.
At operating temp the ecu would be receiving faulty info as there would be unmetered air entering the mix, throwing off the A/F ratio.
Check the big elbow hose between the air filter and the throttle body for cracks and rips as that’s a very common place for an intake leak.

**Mozza1219** · 11-26-2022, 09:08 AM

Could be a partially clogged injector. Mine would be fine on cold start and then after a few minutes would missfire on cylinder 2. Revving it over 3k rpm stopped the missfire but I couldn't drive the car like that. It was bucking and shaking up until 3,000rpm. You can try injector cleaner, but that didnt sort mine out. Had to get the injectors cleaned at a shop etc.

**82eye** · 11-26-2022, 11:46 AM

probably has more than one issue compounding the problem. a faulty or missing 02 sensor definitely isn't helping the cause.

**cole45acp** · 11-26-2022, 01:21 PM

It's not even that it's only happening at operating temp, honestly it's only happening after being driven for periods of time longer than 30 minutes or so. The vacuum leak suggestion is very possible though, I'm currently replacing my intake manifold gaskets because I found that some of the original gasket was completely missing. While during the process I also found that one of my fuel injectors had an o-ring that was broken.

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Originally Posted by Mozza1219

Could be a partially clogged injector. Mine would be fine on cold start and then after a few minutes would missfire on cylinder 2. Revving it over 3k rpm stopped the missfire but I couldn't drive the car like that. It was bucking and shaking up until 3,000rpm. You can try injector cleaner, but that didnt sort mine out. Had to get the injectors cleaned at a shop etc.

That's also possible, I'm getting my injectors professionally cleaned this week (just sent them out today). Hopefully that helps out in a few different areas.

**82eye** · 11-26-2022, 11:43 PM

Originally Posted by cole45acp

It's not even that it's only happening at operating temp, honestly it's only happening after being driven for periods of time longer than 30 minutes or so.

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the description you give sounds like textbook 02 sensor failure

Originally Posted by cole45acp

That's also possible, I'm getting my injectors professionally cleaned this week (just sent them out today). Hopefully that helps out in a few different areas.

they would be due for a refresh as well considering the vintage of any e30.