Just started driving the car after sitting for 15 years. Runs ok except when I go to shift up or down, the engine speed doesn't drop right away when I push in the clutch. It just sits there for a few seconds and will then SLOWLY drop down

Have new vacuum lines on engine and all are tight. Will check again.

Lubricated the pivot points for the accel cable at the gas pedal and the pedal thinking maybe the pedal was sticking. All good.

Adjusted the idle screw. Now at 1000 RPM when engine warm.

Clutch and accel cable are original to the car so they can't be tangled up.

When we were getting the car running again, the aux air regulator would not close, and the engine would run at almost 3000 RPM at idle. Took it off, heated it up, sprayed the daylights out of it with PB Blaster, heated some more, and spring inside finally popped loose. Checked it with power from the battery and it closed when it got hot and opened when cooled.

If this thing didn't completely close off when hot, could that be causing the engine revs to stay up in between shifts?

Could drive it the way it is, but that can't be good. What else to look at??? Would appreciate any suggestions. Thanks.

Ed

I could be way off base, but I would take off the air intake box and watch the throttle body butterfly open & close as the throttle spring actuates it. It could be gummed up & slowly closing. The throttle spring might also need replacing. Just some thoughts....assuming you have FI.

The accelerator cable itself could also be gummed up/deteriorating inside the sheath as well...causing slow response.

Timing too far advanced will cause this
So will the knob on the ecu if it's set too rich. Points advance plate sticking will cause the same symptom

Decel valve is another thing I would check. Simple test is to pinch the hose running into the plenum and see what happens.

It could even be a pressure plate issue. Even a cable issue. Does it diseingage the engine from the transmission? If it is actuating slowly...


If it doesn't do this sitting there revving in neutral you have a clutch issue. Or a pedal assembly issue.

start there - its a simple test.

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My test on the decel valve. Did I do this right?
Took it off the car.
Tried to blow thru the side and rear openings (where the hoses connect) and no air flow. Seems like its closed.
Attached vacuum pump to the small front port and pumped it up to 17 and some air passed thru it when blowing thru the side opening. Got a bit more air flow at 18.
Should I get the same amount air flow when blowing thru the rear and side openings when at 17 or at 18?
Would it make a difference in how the car runs if the valve operates at 17 or 18?
What factory setting if anyone knows?

Thanks for the help.
Ed

3/4 down the page is an explanation of how the decel valve works.


https://members.rennlist.com/pbanders/DJetParts.htm

That’s a decent way to test it. And based on your numbers, it seems a little worn but not broken.
Here’s what I figured out with mine several months back:
http://www.914world.com/bbs2/index.php?s=&...t&p=2958098

Bottom line there, I think you could tighten it up a bit, but I’m not sure it’s the primary cause of your rev hang.

Easy way to find out at the decel valve is working or not. take it out of the loop. cap up the hoses and drive it. I haven't used one in many years.

Both my cars had this problem and it was the decal valve.

normally it is closed.
thats how its meant to work.
it only allows additional air through when it is operated/opened by engine manifold vacuum.
the line that pulls the vacuum and opens the valve is the small diam hose (or is on an L jet).

you are not going to notice any air going through it if you just try and blow through it.
at least i don't believe you will.


i own an 74 L jet which uses the same decel valve as the D jets though possibly plumbs it up differently in detail, but i imagine the principle is the same.

sounds like it needs adjusting to operate and cut off at a higher vacuum level.
there is an adjusting nut on it to do this.

thats why its sticking open and engine revs are staying elevated.
weaker levels of engine vacuum close to or even equal to idle is operating it and letting that extra air in to elevate revs above idle.

as suggested above - disconnect and plug off the small vacuum line to it.
then see if your revs stay elevated or drop to idle suddenly on backing off throttle.

if the revs do drop then its decel valve.
try adjusting it, you can do that by trial and error. a little bit at a time.
Van B did have some vac levels he found that worked and he measured.
that was for an L jet though.

Took the decel valve off the car and made some adjustments to it. Reading the vacuum pump, it now starts to open at 18 and it appears to be well opened at 19. Put it back on the car. The hanging up revs that I had before between shifts are pretty well gone. May play with it a bit more, but good enough for now. Might check the timing again too just to be sure.
Many thanks for the suggestions and advice.
Ed

Dirty advance plates with 40 year old grease need to be cleaned.
The vacuum is pulling back the advance
It needs to move really easy for that to work.

Simple thing to fix.

Glad to hear it. Even though I suggested it, you can see I still doubted it as a contributor based on your numbers. I guess the 1.7 is just more sensitive.

FWIW, I settled at 20" on my 1.8L for initial opening.