M20 acting weird

[e30loverSC]

Im having several odd issues with my 87 325is, recently rebuilt the head. First off, when im driving at a constant speed like on the highway usually 40 + mph, if you go up hill and give it gas to not loose speed the checkengline light comes on, but as soon as you let off the gas it clicks off? And if i really get on it the light will come on. Secondly-Dont be dick, and no i dont go around bouncing off the r3vlimiter. but occasionally ill tap it. Before i rebuilt the head it sounded normal, since i put the head back on its sounds weird, very unclean, and lastl at idle its been running rough, maybe a valve adjustment is need, but idk what the deal it. Timing off maybe? I made suer the marks were lined up though.

[jlevie]

What fault code(s) is stored in the DME?

[e30loverSC]

Stored where?

[e30loverSC]

ok it gave me an O2 sensor code

[Smatt90IS]

haha i read the first post and was about to say o2 sensor mine did the exact same thing last week

[e30loverSC]

Yours was doing the check engine light thing or all of it?

[BergerNJ]

Yours was doing the check engine light thing or all of it?

I am fairly new to the mechanical world, and by new I mean trying to use my hands instead of reading things about cars all day.

But that sounds like an 02 sensor?


I also read that after people rebuild their heads, after about 500 miles they get the valves adjusted to get it perfect. If it were up to me I'd adjust them as soon as I noticed it.

[jlevie]

It could be the O2 sensor, but anything that upsets the A/F ratio (intake leak, fuel problem, misfires, bad MAF,) will also produce a Lambda fault code. The useful life of an O2 sensor is not more than 100j, so it that applies the sensor needs to be replaced. Then have the intake smoke tested and fix any leaks found. Reset the DME by disconnecting the battery for 30 seconds and see if the CEL comes on again and another Lambda code is set.

[E30Nova]

haha i read the first post and was about to say o2 sensor mine did the exact same thing last week

Ditto. When I got the car I had the same symptoms. At idle the light was *usually* off, and as soon as I got on the gas up till around 2000 rpm's, the light came on. Once I hit 2000, it went off.

I tried doing the stomp test and even using a scanner and nothing came up, but as soon as I put in a new O2 sensor to get it to pass smog, bam! No more check engine light.

I'd start with at least a valve adjustment, and like jlevie said, if you don't know the mileage of your O2 sensor, or it's been over 75,000 miles, replace that.

Matt

[e30loverSC]

yea i have no i dea i bought one. And yea since i put the head on i havent edjusted them. I will right as soon as i have time. monday mayybe. THanks alot

[mazzo]

Same behavior

Hi all,

My 88 325i convertible has similar behavior. It run perfectly fine on normal path (no issue with idel, partial throttle or wide open throttle), but once I go uphill, CEL will turn on within 10 sec. If I let go of gas the CEL will go away. But if I continue to give gas CEL will be on until 30 sec after I am done with uphill road.
I cleaned my MAF and made sure my boot / hose has no leak. I clean the ICV and TPS. I replaced my fuel pressure regulator + fuel filter, and I was almost going to replace my crank sensor (I was suspecting CPS is the issue because of its age). I am glad that I found this thread which leads me to think of my O2 sensor and bingo - the sensor has not been replaced for a long time for sure because most of the plastic on the hook up (to the connector) has peeled off, which indicated that it has been sitting around for very long time (I acquired this car without much historical record of it).
I ordered a new O2 sensor and hopefully after replacing that I am good to go. :) Is there anything else I should check, just in case? (I have a walbro pump but not sure of its age / condition, but at least I don't hear any noise from the pump)

Matthew