By the serial number, I have one of the last 200 made for 1976MY.

The fuel system is good:
New injectors
New fuel pump
New fuel lines and fuel tank.

Fuel regulator is working ok.

Runs good with good acceleration.

PROBLEM is:

Idles around 900-1000 when cold. When it heats up, it wants to idle at 1800-2000. My tech says the throttle body is closed and the adjustment screw is all the way.

My tech is a VW bug specialist at repair and restoration, if that info helps.

Looking for suggestions, please?

Thanks

Interesting... My idle tends to drop by about 100 rpm after warm up. Try tweaking the adjustment screw despite what your tech says. Does this part of the throttle body need a good cleaning?

1.8 or 2.0?

Timing

Vacuum Leak

Depends on what engine he has. Aar could be suspect as well, need to know the time frame of 900-2000 shift.

@txbentleyboy
but i would add one more thing, running a bit lean maybe, if timing is set correctly and a smoke test has checked for all possible vac leaks, check the AFR, i had this issue with a rebuilt MPS and it was very lean so idle was fast, but also that idle screw should not be all the way out it should be mostly in, and closed, so just try adjusting that first, then look into AFT and how lean you are running.

Phil

1976 2.0

Feel good about your timing?

Is your vacuum retard hooked up correctly? Do you have a stock 76 distributor?

First and easiest thing to do is pull the inlet hose to the aar and put your thumb over it when the engine is warm. If the idle falls, that needs looking at, if there is no vacuum at your thumb then it is fine, move on to more difficult things. Which we can help with.

What everyone else said.

Also, when did this start happening? Out of the blue, or was something changed/done prior?

I just advanced my timing a little (35 all in) and my idle jumped from 950bto 1250. My idle bleed screw leaks something fierce so I have to plug it with silicon glue to get my idle back down to 950 again. I had it low to be on the safe side while I was tuning the mps.

Does the 2.0 have a decel valve like my 1.8?
That high idle when warm was the first issue I tackled with my car and the solution was to adjust the decel valve to begin opening at 20 in hg of vacuum. It was opening at 15 in hg which was low enough to open at idle and then the increase in revs would increase the vac, which increased the rev on and on until t was 2000rpm.

they do have a decel valve in a 2.0, same as our 74 L jets.
maybe tuned differently. do not know.

whether it creates the cascade effect i don't know,
but thats a very good description you have just given of its compounding behaviour when on the blink in the L jets.

i remember when you brought the problem into the forum and i stabbed a single guess at it. was just a wild and flippant guess. but your approach to nailing it down, tuning it and solving it provided very valuable information to setting one up, considering they can be randomly found on many vehicles of the era as suitable donors.

For sure, you had me at Decel valve hahaha!
That was my first week of ownership and for what I paid, I was pissed at the poor state of tune the car was in. And as a compounding factor, I had no idea what anything was on that car!

yes the guess was flippant since i don't have one on mine and never have.
but it got brought up during recommission.
i made desperate attempts to understand its operation theoretically before deciding that mikes assessment of their necessity to L jet was reasonable advice. ie not necessary necessarily, but absolutely necessary on a d jet. others will disagree very strongly with that, notably mr. p. however he will be pleased to learn i intend to reintroduce the device to my car now that i know i can fiddle with one and get it right thanks to your vac specs. i got one off a 911 and i know where there is another one i can get hold of.
endlessly discarded off 70s 911s in australia and left on shelves or still bolted to the engines hose-less. i even know where i can get them rebuilt (along with fuel pressure regulators) - there is a mob in brisbane who do them.
unfortunately aavs are not something they do. opening them up and doing diaphrams is their speciality. have to be metal cannister type units. puts pcv valves out of the equation too.

You need to smoke test the intake tract and find the intake leak. You are getting unmetered air from somewhere if your idle screw is really fully closed, your throttle plate is not held open, etc.

With the idle screw fully closed the engine should stall and die even when warm.