Should the idle adjust screw on the throttle body completely stop the flow of air into the throttle body? When mine is in as far as it can go, idle will not go below 1200 rpm, but with aircleaner removed, if with my finger I stop that hole from the inside, the idle immediately drops andholds steady at @800 rpm. Smooth and no surge. Seems like it should close off the air flow more. Consider that valves are set, timing set, and dwell and points are right on, as is the t.p.s.(throttle valve switch. Also injector seals, intake runner seals have been checked for leaks, new vaccuum hose kit installed. No leak detected from throttle body but I was going to pull that tomorrow and replace anyway. Also butterfly valve does not stick. Aar good.

Anything else that needs checking? Or is it the idle adj screw?

Thanks

Phil

P.s. it is a 75 2.0 d-jet.

Phil:

I am no expert, but it sounds like you are running lean at idle. With the air cleaner on and everything in place, try using the idle mixture adjustment knob on the ecu. Turn it one click at a time, clockwise (to richen the mixture) and allow the engine to stabilize. Then mess with the idle adj screw.

I have a 74 2.0 D-jet and had similar issues (I could not get the car to idle below 1300 RPM or so with idle adj screwed all the way in). I went back and double checked EVERYTHING tune-up and vacuum related and found something else off. After fixing, I was able to get the idle to 900 RPM using the idle adj screw by adjusting the ECU mixture.

I am sure some of the djet gurus will chime in as well.

Good luck.

thanks, so what was "it" that you found that was off when you went back and re-checked? we (myself and my porsche mechanic) went back to the fuel mixture increase the richness setting at the ecu, but did not seem to correct the problem, so must be missing something.

Phil,
I have heard that the thru holes in the plenum can crack and leak, causing high idle. I don't know of any way to check without removal, maybe someone else could clear that up. Sounds like you have covered all of the other ways that could cause high idle.
Tom

tom,
thanks. my mechanic discussed that possibility yesterday, and decided that we should pull it to see if there is any cracking there, replace if necessary, otherwise re-install with new seals. might be putting a call out for a clean replacement throttle body and plenum.........

phil

If the idle is high, air is leaking in somewhere in addition to the throttle body. Could be anything from injector seals to intake runners not sealed to the heads to a leaking decel valve (you said that you checked the aux air valve) to a split vacuum boot. Really an easy and rewarding fix (the moment you find it!!!)

Running the screw all the way in is not supposed to block all air through the idle bypass passage. There is also the bleed hole in the throttle plate itself.

You've got a leak somewhere. Maybe in the PCV system??

--DD

"It" was the timing and a mis-routed vacuum hose for me. It looks like you have those bases covered though. I used this diagram to double check the routing:

http://www.pelicanparts.com/914/technical_...4_20FI_diag.htm

Update: had trottle body taken out, cleaned new gasket, and went 1 notch richer. Now I'm at 950 warm idle no surging!!! Hope it holds. I think I will leave alone for now but I would love to test another MPS just to see if there is a change. I put this one in when I bought the car . Old one was shot. Got this from injector corp. It is a rebuild I believe. If any one has a spare. For 75 2.0 d-jet. , its the only thing I have not tried yet.

Phil

(

quote name='saigon71' date='Mar 1 2011, 09:47 PM' post='1438731']
[quote name='Philip W.' post='1438394' date='Mar 1 2011, 08:59 AM']
[quote name='saigon71' post='1438385' date='Mar 1 2011, 08:10 AM']
[quote name='Philip W.' post='1438294' date='Feb 28 2011, 11:42 PM']
Should the idle adjust screw on the throttle body completely stop the flow of air into the throttle body? When mine is in as far as it can go, idle will not go below 1200 rpm, but with aircleaner removed, if with my finger I stop that hole from the inside, the idle immediately drops andholds steady at @800 rpm. Smooth and no surge. Seems like it should close off the air flow more. Consider that valves are set, timing set, and dwell and points are right on, as is the t.p.s.(throttle valve switch. Also injector seals, intake runner seals have been checked for leaks, new vaccuum hose kit installed. No leak detected from throttle body but I was going to pull that tomorrow and replace anyway. Also butterfly valve does not stick. Aar good.

Anything else that needs checking? Or is it the idle adj screw?

Thanks

Phil

P.s. it is a 75 2.0 d-jet.
[/quote]

Phil:

I am no expert, but it sounds like you are running lean at idle. With the air cleaner on and everything in place, try using the idle mixture adjustment knob on the ecu. Turn it one click at a time, clockwise (to richen the mixture) and allow the engine to stabilize. Then mess with the idle adj screw.

I have a 74 2.0 D-jet and had similar issues (I could not get the car to idle below 1300 RPM or so with idle adj screwed all the way in). I went back and double checked EVERYTHING tune-up and vacuum related and found something else off. After fixing, I was able to get the idle to 900 RPM using the idle adj screw by adjusting the ECU mixture.

I am sure some of the djet gurus will chime in as well.

Good luck.
[/quote]

thanks, so what was "it" that you found that was off when you went back and re-checked? we (myself and my porsche mechanic) went back to the fuel mixture increase the richness setting at the ecu, but did not seem to correct the problem, so must be missing something.
[/quote]


"It" was the timing and a mis-routed vacuum hose for me. It looks like you have those bases covered though. I used this diagram to double check the routing:

http://www.pelicanparts.com/914/technical_...4_20FI_diag.htm
[/quote]

Like the dr said, it is either timing or vac leak. Disconnect everything except the MPS. Idle good? Start adding back the pieces until the idle goes up. Idle didn't change after pulling everything except MPS....cold start valve or gasket, TB gasket, runner boots, plennum, FI gaskets and so on. You'll find it.

I think we got it! Idle now at 900 when warmed up. no surge!

After setting the valves, we reset the timing, pulled the throttle body and cleaned, resealed, tightened all vaccuum lines and somewhere in there idle is now right on!

Thanks for the suggestions.

I'm now

Doesn't success feel great?
Tom