I finally got my FC started up tonight after a fuel problem (fuel pump assembly, I think - bizarre). The car hasn't run for about 5 months up until this evening. When I fired it up the engine was revving at around 3,000rpm as it warmed up. Sounded a little rough though with some pops in there (but no bangs). But then after about 2-3 minutes the revs just dropped off and the car died. Turned the key and started it right back up again but then unless I gave the car some gas it would die. As the revs got lower the popping frequency increased.

I might have a vacuum leak somewhere in the system which I need to check out in the morning, but until then I was wondering if anyone could suggest any more things I should check out. As always, apologies if this is a dumb question!

 

definatly check for vacuum leaks and check the bypass air control valve per the fsm. it is normal for the engine to rev to 3K on a cold start. it should gradually drop as it warms up, not just fall flat on its face and stall.

 

Will do. To be fair there are probably a bunch of vacuum leaks in the system but I'll check the BAC too, both for leaks and according to the FSM. FC3SPro also suggested putting clamps on the BAC valve hose (http://www.fc3spro.com/TECH/PROBLEMS...NE/leaksv.html) which I'll also do tomorrow.

 

Did some checking this morning and I can't see any gaping vacuum leaks. I also checked the BAC solenoid too and it came out just out of spec (was giving me a resistance of 12.4Ω whereas the FSM says 10.7-12.3Ω is within spec).

But I checked the TPS and closed resistances there out of spec quite a bit:
Narrow range: 2.3kΩ (spec is 0.8-1.2kΩ)
Full range: 1.2kΩ (spec is 0.6-0.9kΩ)

Could this be causing my problems? Don't see how it could be causing the misfires down low which it seems to have. Even starting cold this morning, unless I was giving it some gas it was wanting to die on me straight away.

 

Tried unplugging my TPS sensor today just for a laugh and it still did the same. Changed the MAF and still did the same. Should note that when I checked the TPS above it was with the engine cold and so that might up the resistances a bit I believe.

But then I reconnected the TPS this evening and started it First time it died within 3 seconds. Second time it fired up and decided it was going to idle at 3,000rpm. Was holding there pretty damn steady for a minute or so. Went round to the exhaust and could hear a bit of a misfire still but intermittent. Turned the engine off and fired back up again and went straight up to 3,000rpm. Would have held it there longer but I do have neighbours in my apartment block and the exhaust is facing straight into a wall so it's pretty damn loud!

God knows why it suddenly decided it was going to idle there.

 

The plot thickens with this one. If I start the car normally it will just die on my after a second or two. But if I give it some gas after it's fired up and lift the rpms above about 2,500rpm then it will happily idle up between 2,500rpm and 3000rpm without my pressing on the gas. Like I said before, I can hear a bit of a misfire, but nothing like what it's doing down at 1,500rpm. The car will move like that but if the revs drop below about 1,700rpm it's wanting to die again.

Only other thing to note is that one of the nipples on my PCV broke so at the moment I've got the 2 vacuum lines blocked off and the oil one venting to atmosphere.

 

The 3000 rpm idle is normal for the first 17 seconds after a cold start. This is due to the accelerated warm up system (AWS). The ECU senses the cold condition via the water thermo sensor (behind and below the alternator). If the temp is below a certain value, the ECU commands the air bypass solenoid (low on the left side of the plenum, near the rear) to open a passage for air (via hoses) to bypass the throttle. This will cause the car to idle at 2500-3000 rpm for 17 seconds, after which it should close, and the idle drop to about 1500 (due to the fast idle cam). Once the coolant heats up the thermowax should allow the roller off of the fast idle cam, and the idle should drop to 750-800, where it is controlled by the ECU by varying the duty cycle of the BAC valve.

You should be able to drop it out of the 3000 rpm idle by blipping the throttle once. In any case, if the 3000 rm idle extends past 17 seconds, there is something wrong. Possibly your air bypass solenoid is stuck open. Or, maybe the fast idle cam is so far out of adjustment that it is commanding a 3000 rpm idle instead of 1500 in the cold condition.

Another possibility is a fault with the water thermo sensor. The ECU sees high resistance as cold temp; if the sensor is faulty (high resistance), or the connector is off, or open, the ECU may be seeing that as a cold temp, and in that condition it runs the mixture up very rich thinking that the temp is cold when it is not. The rich mixture may be too rich for it to run at normal idle, and then it dies.

I don't know what year is your car, but the writeup in the 89-91 online manual on the AWS is much more detailed than it is in the 86-88 manual.

Another possibility is a vacuum leak. The rich condition created by the AWS may allow it to overcome the lean conditioin caused by the vacuum leak, but not when the temp warms up and the ECU reduces the mixture to a more normal condition.

 

But the high idle only happens when I push the rpms up to that level to start with. If I just start the engine it will fire for about 2-3 seconds with some misfiring and then die (because it's trying to keep a normal idle). It's almost like something is sticking, which is what I'm going to check out in the next day or 2.

And the car s a '91 model.

 

That sounds an awful lot like a vacuum leak, assuming it is misfiring you are describing, not backfiring. Vacuum leaks have their most severe effects at idle and low power, as the volume of unmetered air coming in through the leak is larger due to the high vacuum, and is a larger percentage of the total flow volume. It may be that the engine is running rich enough (especially right after start) that the mixture with the leak is combustible at 3000 rpm, but not at idle.

I would still check (if only to eliminate) operation of the AWS, fast idle cam and thermowax, BAC valve per the FSM procedures. There is also a spec for clearance between the bore and the primary throttle plates; and make sure the secondaries are closing fully.

And, yes, the TPS is involved in the idle performance. Adjust it back into spec; if you can't, you may have to get another one...