Cold start idle and acceleration issue

[lambo]

Hey guys

So, I've got an issue with my M20. I'll go through the whole history of my ordeal.

For the past few months, before I slid into a curb and had to redo my rear subframe, I had an issue where if I drove my car, parked it for anywhere between 15 minutes to an hour or so it wouldn't start on the first try. I chocked that up to a bad FPR. Never got around to replacing it although I have two spares. Then I wrecked my car, fixed it and now it has this cold start and acceleration issue.

The issue is that when I start the car in the morning it starts up fine, then the revs dive down and I usually have to manually rev it to keep it alive. When I start driving it stumbles on acceleration. However, once it warms up a bit it feels fine, it feels like it's a bit down on power though.

Today I cleaned my ICV and throttle body and I replaced the FPR vacuum hose. I started it up afterwards and it still had the cold start issue. I drove it and it still had the acceleration issue (not surprisingly). I drove it for a few minutes and after it warmed up a bit it accelerates up to redline fine, no stumbling or anything. However, when I stop and it starts to idle it throws a check engine light but when I rev it, it goes away.

I have a few ideas what this whole thing might be. I'm thinking this is a mixture of a bad ICV, FPR, injectors and intake gaskets. I'll replace each of those things and see where that gets me.

This thread is mostly to document my repairs as a lot of the threads I found never offered an actual answer. Hopefully this can help someone else down the road.

If you have any speculations or ideas, they are greatly welcomed!

Thanks!

[lambo]

Here's a video, too:

[lambo]

Found this post by jlevie (from this thread - http://www.r3vlimited.com/board/showthread.php?t=264349):

Without more information about the car, start with:


Idle or hard starting problems are most commonly caused by intake leaks and/or
a sticky or defective Idle Control Valve (ICV). The only reliable method of
locating intake leaks is to have a smoke test run on the intake and crank case
and to test the brake booster with a gage and vacuum pump. The complete list
of possible causes of an intake leak is:

Intake boot
Throttle body gasket
ICV hoses & connections
Brake booster, hoses, and connections
Crank case breather hose
Evaporative control hoses, valve, and expansion tank
Fuel pressure regulator & hose
Injector seals
Valve cover gaskets & bungs
Oil filler cap
Dip stick o-rings
Oil return tube o-rings

While leaks in some of those can be found by inspection or by spraying carb
cleaner on suspect areas, not finding leaks that way doesn't eliminate the
possibility. Only a smoke test will really work.

Once the possibility of intake leaks is eliminated, the ICV needs to be
removed and cleaned with carb cleaner until the vane inside moves freely. When
the ignition is switched on you should be able to feel vibration from the
ICV. If no vibration the ICV is bad, there's a problem with its wiring or
connector, there's a problem with the TPS, or the DME (or Idle Control Module
(ICM) on an ETA car) is faulty.

For the DME (or ICM) to control idle, the idle switch in the TPS must work
correctly. The switch should close when the throttle stop is 0.030- off
the idle stop screw.

The fuel system should be tested via the suite of tests in the Bentley manual
as invalid rail pressure can be a contributor to idle and starting problems. A
simple injector check is to pull the injectors, jumper the fuel relay to run
the pump, and see if the injectors are leaking. You can also point the
injectors into a towel, remove the coil wire, and crank the engine to see if
all of the injectors appear to be spraying in a similar fashion. The best
approach to possible injector problems is to have the injectors cleaned and
flow tested. Since raw fuel can or will be released in these tests, have a
fire extinguisher handy.

While a bad check valve in the high pressure pump can result in longer than
normal cranking, if the fuel system is working as it is supposed to the rail
will reach normal pressure in a few turns of the engine. A weak pump, clogged
filter or leaking FPR in conjunction with a failed check valve can result in
longer cranking.

The O2 sensor can be a contributor to idle problems. The O2 sensor is a
scheduled maintenance item with a useful life of no more than 100k. If the
sensor has that mileage or more (or is of unknown age), replace it.

The AFM can be a contributor. If the vane doesn't move freely or the
resistance track is worn the DME may be receiving invalid data from the
AFM. And if someone has fiddled with the bypass air adjustment the DME may be
unable to stabilize idle. The bypass air adjustment should only be adjusted
per the procedure in the Bentley and with an exhaust gas analyzer. And even
then everything else associated with engine management has to first be
operating properly. If the AFM becomes a suspect, replacement with a good used
unit is the best approach.

Improperly adjusted or malfunctioning valves will affect idle and starting. As
can compression issues from ring or cylinder wear. A valve adjustment is
called for every 15k. A useful diagnostic is to run compression (dry and wet)
and leak down tests on the engine. Aged ignition wires, plugs, distributor
cap, or rotor can cause problems. Insulation does break down with time and
heat. And since the youngest E30 is going on 20 years old, if the ignition
system is original or the plugs are old replacement is indicated.

Although not usually a problem, a bad DME temp sensor is a possibility. That
generally won't cause an unstable idle, but can cause hard cold or hard hot
starts and/or a rough idle. As can problems with the timing reference
sensors. Although not commonly encountered, a bad harmonic balancer on an
M20B25 or M30 engine will cause problems.

When all other possibilities have been eliminated and idle or starting
problems persist, replacement of the DME, or if applicable the ICM, is
indicated.

Good info.

[lambo]

Replaced my icv with a known working one. Didn't change anything but I didn't really expect it to.

Just updating this thread with anything I do.

[Tom.]

How old is your o2 sensor?

[lambo]

How old is your o2 sensor?

No idea. That is one thing I still haven't checked.

[lambo]

So I finished working on my car this morning. Rough idle is gone, CEL is gone, cold start idle and acceleration is gone. It's a good day.

Turned out my rough idle and CEL were being caused by this guy. It's a vacuum line that goes from the TB to the charcoal canister. It wasn't even plugged in.



I think it was fully unplugged when I pulled the TB to clean it, I didn't even see it. It was missing a hose clamp so I'm thinking it was barely being held on in the first place.

Anyways, now she runs beautifully. Idle is damn steady, like new car steady, at 700ish RPM.

Here's a list of all the stuff I replaced/repaired:

- Intake Gaskets
- Vacuum Hose (from intake to FPR)
- Injectors (refreshed M50 injectors)
- FPR
- Fuel Lines
- TB Gasket
- VC Gasket
- Valve Adjustment
- Spark Plugs (NGK 5077)
- Air Filter
- Cleaned a lot of electrical connectors

I bought a new fuel filter but I haven't installed it yet. I might not because I replaced it only 2 years ago.

[tsouth]

Glad to see you've found the issue, and a simple one at that! Congrats man.