jwillman

Been trying to get the CIS sorted for a while.

What I have done:

Top end refresh, seals and intake cleaning done this summer.
New MB short injectors installed two weeks ago.
New plug wires in October.
Bosch OEM cooper plugs this summer.
Tested fuel pressures and w/i tolerance 2 months ago.

Problem:

Car starts immediately when cold but idle is erratic for the first 5-10 seconds and then stabilizes at 1400. As it warms idle drops to ~800.

When turned off and immediately started no issues.

If I come back an hour later the car turns over but is very hard to start requiring throttle input to come to life.

I plan to recheck pressures tomorrow.

Do my symptoms point to something I have not checked/ done?

AirtekHVAC

Accumulator? Not sure what pressure remains after an hour....but....that is its job.....

Jadz928

Yep. That and/or fuel distributor bleed-out. Get out the gauges and report back.

Doug_B_928

This sounds very similar to my car. The only difference from your description is that the "hour later" starting problem in my case would only occur if the car has been driven and turned off hot, in which case I put the throttle down on startup and it sounds like it momentarily blows out a clog and then runs great. My next step for when I have time is to adjust the WUR (I think my cold control pressure is low IIRC). I've changed the fuel check valve, accumulator (was bad but didn't solve the problem), had the cold start injector tested, and tested the auxiliary air regulator. The one anecdotal thing I did notice was that the cold start problem doesn't occur when I have the vacuum lines disconnected on the WUR. You might want to try that just for fun to see it the same happens in your case.

jwillman

OK, tested pressures today.

Outside air temp was 58 F and WUR temp with IR gun was 56 F.

System pressure (valve closed) - 75psi

Leak down (valve closed)
Start - 46 psi
10 min - 35 psi
20 min - 30 psi
30 min - 25.5 psi

Cold pressure (valve open) - 19 psi with WUR at 57 deg F

Leak down (valve open)
Start - 43 psi
10 min - 32 psi
20 min - 26 psi
30 min - 20 psi

Warm pressure ( key on and WUR connector attached)
start - 19 psi
warm - 38 psi (took about 10 minutes to get here)

And the experts say?

Jadz928

Your cold pressure is very close at 19psi. Should be 20psi at 56 deg. Warm pressure is fine at 38psi with vacuum disconnected (should read 41-46psi connected, w/engine running)

If your injectors are new, next look at your fuel distributor.

What I'm finding is the metal diaphragm plate in the FD has fatigued... on some but maybe not all 8 ports, causing some injectors to open early and close late... bleeding fuel.
This makes it very difficult to tune properly for all conditions. An exhaust gas sniffer doesn't tell the whole story because it meters the burn of all 8 cylinders. I can see this issue on my FD bench tester.

I call it a 'tired' fuel distributor. The metal plate has fatigued to the point where it can't seal (or hold-back) fuel at the ports any longer. This is why I use a new plate for my rebuilds.

There's a couple different ways to test this on the car. However, I suggest this only for advanced CIS tuners. Matter of fact, I'm not going to post it here. If this is something you are willing to attempt, contact me via email or website.

AirtekHVAC

Good luck..I rebuilt mine....took me 5 tries, I flooded the engine, lost some parts...

Got her running great right now, but still not tuned right.....of course I have not really messed with it either.....

Unless you really want to....see if you can talk Jim into doing it for you...

jwillman

Update.

I completed the checks Jim Doerr gave me and the FD seems ok.

That said on reassembly I noticed that one of the banjo bolts had a filter inside it that floated up and down the length of the bolt. It dropped out with some tapping and seemed clear (could see light through the filter) but as I did not see them in the others I left it out. That said I did not inspect the others as they were already assembled.

Not sure of the implications of having some in and others missing?

Drove the car this morning with temps at low 30's. Car started as it has been, started immediately but took a few seconds to stabilize at idle. I let it warm up and then noticed warm idle was surging/ hunting between 400 and 800.

Drove the car to work and ran fine except the idle was very low at stops to the point that it would die if I did not assist with accelerator. Once on the toll road it ran fine at 80ish and once I pulled into the parking lot at work, 10 mile trip, the idle was stable at 900ish.

Went out a couple of hours later and it started right up and drove and idled fine.

I have also noticed on first start of the day that high idle seems to vary in that it will stabilize at 1200 and if I rev it a bit it comes back to 1400 rather than 1200.

What controls cold high idle versus warm idle adjusted at the throttle body?

Any thoughts on what caused the hunting idle issue I saw this morning?

Jadz928

The aux air valve controls cold idle.

Besides checking AAV function, check for vac leaks at hoses and seals. Unmetered air will raise idle (and can be intermittent, when as it warms up and things change).

No sure about one filter being removed on the FD. Never done that. I remove them all.

jwillman

I checked the AAV function the first go around with the WUR. Its opening and closing when tested in the freezer and then mechanically warmed and electrical heater element works.

I did the top end refresh last summer and replaced all the intake runner gaskets, injector seals and various o rings an seals for the FD and throttle body as well as checking all the vacuum lines.

Whats the best way to check for vacuum leaks? I have a mighty vac hand pump.

I had the FD off just after I got the car and did not take it apart but remembered looking for the 8 port filters. Obviously missed at least one. Guess I need to dig into it again and make sure I did not miss any others.

GlenL

Cheap cigar.

Blow the smoke into a line, like the vacuum to the brake booster, and look for wisps of smoke coming out.

jpitman2

Looking for air leaks around the inlet, while its running, spray something lightly flammable (wd40 etc) around each possible joint, and if its sucked in the idle should change perceptibly.
jp 83 Euro S AT 56k

jwillman

What about other components. Anything to check on the throttle body it self or the vacuum limiter?

jpitman2

Check (if fitted) temp switch on heater outlet elbow that is used to trigger slightly rich on warm starts - only energised while cranking, it fires a solenoid nearby to lower control pressure. I had a similar half hot issue on mine, this switch was closing but with 20 ohms resistance, didnt leave enough volts to fire solenoid. Similar spec switch used on 924, but different thread. Also check that nearby solenoid is OK.
jp 83 Euro S 56k

jwillman

In reviewing all the work I did during the intake refresh last summer one thing I am questioning is the paper gasket that goes between the intake spider arm and the engine (39).

I installed it dry. Should I have used a sealant on either side or both?