M20 running rough after head job

[Ceeker]

So, I get the car all together, all vacuum lines checked and clamped. Start the car and of course runs crappy the first while until the dme sorts things out. Then I hear a rattle, almost like a bottom end knock happening. Immediately I start going through my check list of things I did and what I might have forgot. Head was rebuilt and valves were adjusted properly.
All new gaskets etc.

I call they guy and ask him if his idle was shit before the rebuild and he says it was. So this lets me off the hook. it wasn't something I did. I took out his ICV and ultrasonically cleaned it along with carb cleaner. I took off the throttle body thinking it might be a faulty TPS and installed another. No change.

The car is a 5 spd so I know the idle rpm should be around 800
But currently it's doing about 600-650. it is stable but sounds rough. I know this is correct for auto's

any ideas would be helpful.

just so there isn't a repeat of suggestions I have checked the following:

all vacuum related components related to the build and engine. there are no evident vacuum leaks. Did a smoke test as well.

Did a tune up with fresh gaskets all around.
Did a correct valve adjustment cold. .010 TDC.
timing is BANG on. I triple checked timing marks with the belt before installing everything.

[Ceeker]

M20 running rough after head job

So, I get the car all together, all vacuum lines checked and clamped. Start the car and of course runs crappy the first while until the dme sorts things out. Then I hear a rattle, almost like a bottom end knock happening. Immediately I start going through my check list of things I did and what I might have forgot. Head was rebuilt and valves were adjusted properly.
All new gaskets etc.

I call they guy and ask him if his idle was shit before the rebuild and he says it was. So this lets me off the hook. it wasn't something I did. I took out his ICV and ultrasonically cleaned it along with carb cleaner. I took off the throttle body thinking it might be a faulty TPS and installed another. No change.

The car is a 5 spd so I know the idle rpm should be around 800
But it currently it's doing about 600-650. it is stable but sounds rough. I know this is correct for auto's

any ideas would be helpful.

just so there isn't a repeat of suggestions I have checked the following:

all vacuum related components related to the build and engine. there are no evident vacuum leaks. Did a smoke test as well.

Did a tune up with fresh gaskets all around.
Did a correct valve adjustment cold. .010 TDC.
timing is BANG on. I triple checked timing marks with the belt before installing everything.

[russhixmo]

Computer may not be adjusted for it yet. Computers are always trickey

[Ceeker]

Computer may not be adjusted for it yet. Computers are always trickey

you didn't read my post carefully...the car was doing this before the rebuild. :-)

[jlevie]

If the engine passes a smoke test of the crank case and intake that was done properly with at least 2psi of pressure maintained for a few minutes, then I'll agree that there ar no intake leaks. With the other work that you did the possibilities then become a fuel system problem, aged ignition components, the DME (or in the case of an ETA the idle control module). At this point I would want to know what the rail fuel pressure is and I'd want a fresh O2 sensor, ignition wires, distributor rotor & cap, and correct & fresh plugs.

[jlevie]

See your other post.

[Ceeker]

ok, I know the cap, rotor, plugs are to spec and new. proper bosche spark plugs. I can't say anything about the wires, look original. and I don't know the condition of the o2 sensor.

As for rail fuel pressure? I don't have experience in knowing how to test this.
I was thinking possible dme issue. I do have one and easy enough to install to test.

I read somewhere recently that one thing overlooked often is the TPS module which can be adjusted to correct similar issues.

[MR 325]

Do not post two threads for the same topic.

[io_RobbieRodgers]

Take some MAF electrical cleaner and spray the MAF and O2 sensors clean, then reinstall them. It's a real cheap alternative to replacing those things. Do you think it could be worn piston rings as well?

Also, check the white main relay. It could be burnt up, causing the computer to be unable to control things properly. I checked mine the other day and it was pretty discolored. A lot of people swear their cars run like new after replacing the main relay.

[Ceeker]

Take some MAF electrical cleaner and spray the MAF and O2 sensors clean, then reinstall them. It's a real cheap alternative to replacing those things. Do you think it could be worn piston rings as well?

Also, check the white main relay. It could be burnt up, causing the computer to be unable to control things properly. I checked mine the other day and it was pretty discolored. A lot of people swear their cars run like new after replacing the main relay.

thanks, I'll check into that and let you know.
I doubt the rings are worn as there is no oil blowing or burning. these bottom ends rarely see that sort of crap. they are impressive as I have rebuilt my share.

[Ceeker]

ok so here is the update:

I did another smoke test to make sure I didn't miss something - no change
I changed the main relay, AFM, - no change.
I removed the TB and Adjusted the TPS -little change -idle went up to 900-1000 rough spot went away for the most part but it still returns.
Removed the DME and replaced it - no change.

totally stumped on this one.

[jlevie]

When you did the smoke test did you plug the exhaust, use an adapter in place of the AFM and hold at least 2psi of smoke in the intake for at least 5 minutes?