1995 S50B30US - RPM float, running rich, occasional backfire

[bonobo]

Hey guys, I'm having some trouble with my s50, there's a lot of people here more knowledgeable than me here, so I figured I would give the forums a shot. The engine just happens to be stuffed into an e30 if that affects anything.
Stomp test gives code 1444 (no faults stored)

Here's a video of the rpm's sticking, each one is a result of a single, quick tap on the throttle
like I said in the title, the car is also running VERY rich and backfiring occasionally.
I'm pretty stumped, and really just want to drive my car again.

Thanks in advance to anyone who responds!

https://drive.google.com/file/d/0B6pvgs1Ar6fTYk9XR1BCR3YwNzA/edit?usp=sharing

[RobertK]

First check for vacuum leaks and the ICV to be sure its not sticking. Then check the TPS and your wire harness to insure everything is plugged in where its supposed to be.

Also check your throttle cable to be sure your throttle body is closing all the way (push it closed and see if the idle changes). If those don't fix the issue then swap the ECU with a known good one and if how it reacts.

[bonobo]

All my vacuum lines/o-rings are brand new, but I'll go back and smoke test it to see if I missed anything. I also cleaned the ICV when I had it out, everything moves around freely. I messed with the throttle stop screw a little bit during the swap, could that be throwing off the readings from the TPS?

[e30austin]

Is the motor stock? DME running a stock tune?

[bonobo]

Stock engine, red label 413 DME with an eBay chip but it received multiple positive reviews from m3 owners

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[e30austin]

That would be part of your issue. Get rid of it and go back to a stock tune.

How's your MAF? CTS? 02 sensor?

[bonobo]

I will as soon as I can find a stock chip, they're actually pretty hard to find actually. MAF came from a car with no (running) issues, and o2 sensor is new but might have suffered from the engine running so rich. Whats a CTS?

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[e30austin]

Or another tune that is properly suited for these motors, doesn't have to be a stock tune (but it is recommended), could use a TMS, TRM, etc. eBay chips are garbage. CTS is the coolant temp sensor that goes to the DME. When coolant temp reaches a certain level, it tells the DME to lean off fuel.

It sounds to me like a combination of things, but I would check out MAF, 02 and CTS, as well as get a new chip.

[bonobo]

Yeah, I replaced the coolant temp sensor too when I had the engine out. I would rather have the stock chip anyways, I'll keep my eyes peeled for one.
Thanks!

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[e30rapidic]

i've got a stock red label 413 chip that I've loaned out. If you don't find one in the next few days, let me know.

have you messed with the timing or anything? Engine sounds "off"

[bonobo]

i've got a stock red label 413 chip that I've loaned out. If you don't find one in the next few days, let me know.

have you messed with the timing or anything? Engine sounds "off"

Thanks, but I would need a tune for an s50, I'll put up some WTB ads for a 506 tune.

I know what you mean about the engine sounding "off." When I replaced the head gasket I had to re-do the cam timing, but after I replaced the spark plugs (after this video was shot) the engine smoothed out significantly. For some reason, only cylinders 1 and 2 had fouled spark plugs. I really hope it isn't an injector issue, I bought a "refurbished" set...

[bonobo]

okay, messed with the idle stop screw a little more. RPM doesn't float anymore, and the car does not run rich at idle (a little under 750RPM) either. There is still the occasional backfire the car still smokes when the throttle is depressed. Anyone have any ideas?


EDIT: Took the car to 6k and finally got the car to throw a CEL, stomp test gives codes 1222 (o2 sensor) and 1243 (crank position sensor) both parts are new...

[RobertK]

1222 is a basic O2 reading lean code. This usually indicates a vacuum leak somewhere.

As for the CPS check your crank dampner to be sure its mounted flush and not loose. Then check the sensor too. If its a cheap plastic AuroZone chinese sensor I recommend taking it back and getting an OEM CPS.

[bonobo]

1222 is a basic O2 reading lean code. This usually indicates a vacuum leak somewhere.

As for the CPS check your crank dampner to be sure its mounted flush and not loose. Then check the sensor too. If its a cheap plastic AuroZone chinese sensor I recommend taking it back and getting an OEM CPS.

When I looked up the code I read that it meant rich or lean. I'm definitely still running rich, the car doesn't smoke/run rich at idle anymore but it does under throttle. Still can't figure out why

I'll go back and check out the damper and sensor and clear the codes. I don't remember the brand of the sensor (I think I got it at pelicanparts) but if I get another crank sensor code after that, i'll swap it out for an oem one

[RobertK]

The backfire is a result of it running rich under load. You might just have a bad O2 sensor. 1222 is a very vague code. I usually run into it when someone has a vacuum leak. But unfortunately OBD1 is too stupid so all it can throw is a basic fuel mixture code.

You mentioned you purchases some refurbished injectors. Have you installed them yet?

We have a 2.8l M20 stroker that has been spitting / sputtering / running rich and flooding the engine at times. Turned out the CPS signal was crap.