Random misfire concern

[Bggdnssnguy]

Hello again.
So this weekend I decided to do some replacing of a few parts and now I'm in a pickle.
I replaced the MAF with a reman a-1 cardone Bosch maf. The old one had a crack at the base of the wire that reads the air.
I also replaced the spark plugs with ngk plugs that were recommended. Y a couple of people.
And both temp sensors. Blue and brown one.
I put a new radiator in at the same time, and couldn't put the aux fan switch in, I need a newer style switch.

Okay here are the symptoms. On cold start it will run fine, start up great. And then once it gets around to operating temps, it will develop a small misfire. CEL will illuminate. But as soon as you barely touch or stomp the throttle. The light will shut off. And it will run fine for a minute or 2 and then do the same thing. It drives fine under load. Just at idle. In gear or in park/neutral. When car is hot, it will stumble and sound like it's misfiring but no CEL and will rev like a dream and then return to stumble and eventually idle decent with a CEL. And repeats the whole process.

I asked Facebook R3V, and a guy told me he had similar problem and he gapped his plugs to .04 instead of .028 as the book says. I did this and no change. Plugs are torqued to spec. 22ft lbs... being a tech, this is stumping me, didn't do this till I replaced all this.. any help would be appreciated..

[dnguyen1963]

My first guess would be vacuum leaks. Did you do a stomp test to pull the code?

[Bggdnssnguy]

Already check vacuum leaks. They are good. And no cause the check light never comes on until it does the small misfire then goes right back off.

[dude8383]

How old is the cap and rotor? Have you checked them both? How about the coil? o2 sensor?

[Bggdnssnguy]

Haven't checked the cap/rotor or coil.
I just replaced o2 sensor a 1,000 miles ago.
What gets me is that the car ran great with the shitty autolite plugs. Now I put ngk plugs in. It's running like this.

Idk how old the cap/rotor/wires are. But I don't want to just throw parts at it and hope it fixes it. Ya know..

[Bggdnssnguy]

Could putting nickel plugs in and not copper plugs make a difference enough to cause a tiny misfire? But still rev and have power like it did before?

[Bggdnssnguy]

Do these cars need to be cleared of long term fuel trim? I know newer cars do, at least nissans.

[Michael Star]

Could putting nickel plugs in and not copper plugs make a difference enough to cause a tiny misfire? But still rev and have power like it did before?

I haven't found these motors to be that picky on plug choice. Vac leaks are the big misfire issues on these motors

[dnguyen1963]

If the car ran great before all this work, I would put the old parts back in to see if the symptoms go away (yep, a lot of time but your car is not running now). If it does run like before with old parts then change one thing at a time. When you change multiple parts at the same time, it is impossible to diagnose. Just like in science, change one variable at a time. Keep in mind that these engines are old and you can definitely create new problems when working on them.

[MR E30 325is]

This problem reminds me of an issue I had with my E30.

Ended up being the temp sensor that sends info to ECU.

Does the car start fine when it is warm? Mine would start like crap if it had been running recently.

[Bggdnssnguy]

This problem reminds me of an issue I had with my E30.

Ended up being the temp sensor that sends info to ECU.

Does the car start fine when it is warm? Mine would start like crap if it had been running recently.

Yes mine runs like shit when warm and revs amazing even when it's running like shit at idle.


The brown one is the one that sends signal to the Ecu for fuel control.

[Bggdnssnguy]

If the car ran great before all this work, I would put the old parts back in to see if the symptoms go away (yep, a lot of time but your car is not running now). If it does run like before with old parts then change one thing at a time. When you change multiple parts at the same time, it is impossible to diagnose. Just like in science, change one variable at a time. Keep in mind that these engines are old and you can definitely create new problems when working on them.

Well I threw the plugs away. Cause they were turds.
The maf had a core on it. So I turned it in.

And I know it can cause problems. It just blows my mind that these 4 things caused problems.

[dnguyen1963]

Nothing on the E30 surprises me anymore. You just have to be methodical in troubleshooting these problems.

[e30davie]

leave the new plugs in.

"Okay here are the symptoms. On cold start it will run fine, start up great. And then once it gets around to operating temps, it will develop a small misfire"

This to me tells me the problem might be with the new coolant sensor you put in. perhaps its not getting the signal that the engine is hot, so is running pig rich when at operating temp causing your misfire. Also you might have damaged a wire in your loom when changing the temp sensor, the wires in that area on my car are completely stuffed.

Why did you change the coolant sensors? did you have a reason to think they were broken?

[Bggdnssnguy]

To me it seems like a lean condition misfire. As soon as it's hot and idling with the CEL. Put it into drive or reverse and it riches the condition. The light goes off for around a minute or so.

If the wires were damaged. I would think it would throw a light all the time. Regardless. Cause if it wasn't getting a good signal cause of a wire. Then it would throw a light when cold and hot. That's been my experience as a tech. I replaced the sensors cause of unknown condition and I had coolant drained for the radiator change.

All I did was simply pull the plugs off, pop the injector harness off, took sensor out and put new in. And rolled from there.
I got a measurement of ohms at certain temps and will diagnose that this weekend. It's always possible I got a bad sensor. Just cause it's new, doesn't mean jack squat to me anymore.