M20 runs rough like it's got a lumpy cam

[Ceeker]

Hey, so I've swapped heads a few times no problems; I just did another head job timing belt blah blah blah. :-) Car starts ran fine.. I did a med to tight cold 10mm valve adjustment before the head going on the car. Today was the first time taking it out. Sure I could tell idle was a bit off and figured it was the valve adjustment again - no biggy.

Question: could this make the car run rich and trip the engine light?
also, it would buck at certain times while in gear holding a steady rpm.

wondered maybe the afm or dme or 02 sensor cause any of this?

ps. I just got this car so I don't know the history on it.

car is an 89 cabrio 5 sp. thx.

[Hooffenstein HD]

Sounds like intake/vacuum leaks.

[Ceeker]

Sounds like intake/vacuum leaks.

done this too many times. Vacuum leaks would have made it run crap from the beginning. I'm very thorough in my work.

[Ceeker]

Bump

[ahlem]

injectors need cleaning or cap and rotor need replacing or CPS is on the way out or O2 sensor is on the way out. What are the compression numbers? Got an extra coil and wires to swap out? Got an extra set of plugs? How old is the gas in the tank?

[Ceeker]

car ran fine with the present injectors before I did the head;
changed cap and rotor - new
correct plugs - new
Gas is fairly new - but I am thinking of running it to empty and throwing prem into the tank and take for a good run.

I do have a new coil and wires; but again the car was running fine before the top end rebuild so I don't see how that can suddenly make it run shit.

the car passed emissions so I doubt it's the sensor or cat.

thanks for the suggestions folks

[Ceeker]

update: now it runs like shit on start up too;

When I unplugged the AFM the car runs much smoother. Could this be then a fault with the afm or dme?

[trapical]

We're having the exact same issues.

[ahlem]

I had the same issue when I didn't plug in the AFM by mistake after I swapped a head.
There are write-ups about bad AFM's and diagnosing them.
I'd try wiggling the AFM door and contact cleaner on the AFM plug to see if you can localize the issue. Do you have access to a spare?

[redlightpete]

You need to adjust the valves after installing the head. They tighten up when you torque the head bolts. It will run smoother cold because it is richer.

[Ceeker]

I had the same issue when I didn't plug in the AFM by mistake after I swapped a head.
There are write-ups about bad AFM's and diagnosing them.
I'd try wiggling the AFM door and contact cleaner on the AFM plug to see if you can localize the issue. Do you have access to a spare?

After removing the AFM I had found the door was stuck open. used carb cleaner and it released to closed position. Reinstalled it and it runs the same as before; however, the car is idling a wee bit rough and suspect it is something else as it is still burning rich.

I unplugged the 02 sensor to see if anything changed.

Should the idle change when unplugging it?

result: no change in the idle when I unplugged it.

[Hooffenstein HD]

Should the idle change when unplugging it?

result: no change in the idle when I unplugged it.

Did you reset the ECU when you did this?

[Ceeker]

Did you reset the ECU when you did this?

No i didnt diconnect pwr to the dme. I thought if i did that it would have to relearn everything and of course runs crappy again. The car runs pretty good. No hesitation just a bit off and does runa bit rich.

I suppose i could let it reset

[cabriodster87]

Readjust the valves, they may be a bit tight.

[CENTURION]

my m20 had the same issue. now... I changed my o2 sensor, had a valve adjustment, replaced water pump with new, except the injectors were replaced with non v m50 injectors and ecu was not reset. so in the end my motor seized and cylinder 4 or 3 rod broke from the piston. soo... that is what you shouldn't do. hopefully this helps and guides you towards the proper repair. GL