Engine idle raise drop, cold… DJet help.


My 1.7 when started, the idle will go up and down, even for about an hour of driving. After an hour (here or there) the idle stays up and drops for awhile. And then it is fine… but can drop back down sometimes. On hotter days, it seems like it is faster to a normal running idle.

I had 4 ideas:

1.)Cold temp sensors, I know there are 2 but I am unsure about it. Or how to test.
2.)Fuel/vacuum. This was my 1st thought, so I have new lines around the motor and the top of the tank. And the injectors have been re-built. but still could be djet.
3.)I have a really old muffler that needs replacing. warms up, can breate...
4.)Air in. (I know ill start some fights here, but it has the oil mess, I swear it can not get enough air)

Any ideas? It’s a daily driver, and it is annoying as heck.

have you rechecked the MSP? is it holding vac? if not- probably the cause , but i'd next recheck all vac hose connections, and reverify the AAR is working right.

pw

MSP and AAR?

Check your TPS setting and make sure youare really using the idle curcuit.
Look at PP site, or Anders Djet site for the proper ohm meter test to ensure you are using the idle circuit when at idle.

Rich

Location for the resistance values of the sensors, you can get that information on the PBAnders site, its all there,
also some of the bosch d-jet manuals are available on Jeff Bowlsby's site.

Vacuum leaks.

That too.

To expand on this.
I do this to find the leak...which could be anywhere in any vacuum circuit.

Remove all vacuum lines from the plenum and cap them off with rubber caps from NAPA/FLAPS, whoever.

Leave just the mps vacuum line attached to the plenum.
Does the problem still happen?
If no...
Start attaching ONE line at a time until you determine which system is creating the vacuum leak.
Could be the AAR, could be the distributor, could be devel valve...
Do only ONE at a time to do proper troubleshooting.

Does the problem still happen with all lines off?
Yes

Set your TPS per the PP article.
Check to ensure your MPS holds a vacuum properly and does not leak.
Set your points, timing and dwell.
Check and replace the injector seals (vacuum leak)
Check and tighten your intake manifold to head connection (vacuum leak)
Check and tighten the large rubber hoses at the intake tubes to plenum connection.

Rich

i thought it was vac lines as well, but i replaced them all.

i will try what you guys say.

what =

AAR (Auxiliary Air Regulator)
MPS (manifold PS)
TPS (Temperature Sensor)

PS im assuming is Pres sens...

is this correct?

MPS is manifold pressure sensor...the little pinapple looking thing mounted under the battery.

It needs to hold a vacuum.
Test is on the Anders Djet site.

The other leaks that often get overlooked are the intake manifold and injector seals.

Also...clean your distributor and re-grease the advance plates...that is super cheap and will blow your mind while you chase things...when its a simple fix.

Rich

the TPS is on the front of the throttle body- a black plastic cover , opposite side of the throttle return spring. this has circuit board that gets worn or dirty, sometimes just needs to be cleaned off so the contacts will signal the throttle position properly, allowing for proper idle. - if you car bucks sometimes when under a steady rpm , say 3000 steady and you feel that it is most likely a tps issue.

Cool, thanks guys.... this will keep me busy on saturday. and yes, i have already cleaned my distributor...

You're assuming new lines = not vacuum leaks. Never assume anything.

There are plenty of other places to find vacuum leaks.

Hunting idle means lean, which probably means vacuum leak below the butterfly. Don't waste your time with the MPS because if there's a vacuum leak there it will run rich, not lean.

where is this butterfly you speak of.

The throttle plate in the throttle body. The round "butterfly valve" that pivots as you open the throttle.

Since the throttle is closed at idle, vacuum leaks at idle are being drawn between there and the intake valves. So anything that taps into the intake airstream in that area is a potential source for vacuum leak. In addition to hoses, that means...

Throttle plate pins
Seal between throttle body and plenum
Crack in plenum
Seals at plenum to intake runners
Phenolic block between intake runners and heads
Injector seals

...you get the idea

Does the idle hunting oscillate quickly, like once a second? Or is it slow like once every 5-10 seconds?

What is the highest RPM it idles at?

every second. i think it gets to 3k,

but eventually it will get to a proper idle. and stay like that, thats whats weird about it.

That's a pretty significant vacuum leak. Does turning the air bypass screw (at side/base of throttle body) all the way in (clockwise) make a noticeable difference?

i dont mess with it alot because i hate the damn oil bath so damn much. its such a pain to fiddle with it.

i can check that though....

Make sure the o-rings around the injectors are not deteriorated. all you have to do is try and move the injector up and down. if it moves, new o-ring on the injector.

With the engine idling, spray carb cleaner on all hoses, interfaces. When you hit the leak, the engine note will change.