screamin_conure

Still chasing down a crazy idle bug on my '92 coupe, but I THINK I may have discovered a MAJOR clue today as to the source of the problem.

First, a quick background. Within the last two weeks, my car has had new 02 sensors installed, a new fuel filter, and new Bosch III injectors from FIC. Last year when we purchased the car in the fall, I had a new water pump w/t-stat, new intake gaskets, new serpentine belt, new air filter, new PCV valve, new IAC valve and IAC passage cleaned out.

When we first bought the car, the idle was WAY out of whack. It idled well over 2,000 RPMs in park and over 1,000 in gear at a stop. With the new IAC and a clean throttle body done last year, the idle now seemed to be too low, and kinda' hunted around a bit, often times going from too low to too high, and requiring a firm foot on the brake at a traffic light, but still nothing as high as it was when we first got her. This is the way I left it before continuing my troubleshooting this spring. As I mentioned, so far this year, I've put in new 02 sensors, a new fuel filter and the Bosch injectors, but the sometimes low, sometimes high, and always "throbbing" idle still remained. In recent sessions with my scan tool done after replacing the injectors, my left bank BLMs are still a bit high at idle, right around 140, while my right bank BLMs are bang on at 128 at idle.

Today, I took the car out and saw that I was down to just under a 1/4 tank of fuel and decided to gas up. I had been driving it for about a half hour or so when I pulled into the gas station, and by that point, the car was idling at about 1,200 RPM in park when I pulled up to the pump and shut it off. I got out and began to unscrew my gas cap, and as I was doing so, what seemed like a LOT of pressure was releasing from the tank. It seemed that as long as I kept on unscrewing, it kept hissing, until I finally removed the gas cap. I went ahead and filled up with 92 octane, and started the car. Now, the car struggled mightily to maintain 500 RPMs stopped in gear, and was shaking pretty good. It was a classic "I'm not getting enough fuel" kind of idle. It never did die, and when accelerating seemed to run just fine. All of this got me to thinking; this might be some type of fuel delivery problem.

So I took the car home and grabbed my fuel pressure gauge. After thoroughly dousing my hands with the spray from the Schrader valve, I got the gauge hooked up. While moving some vacuum hoses aside to get at the Schrader valve, I gave the fuel pressure regulator vacuum line a sniff and I could smell just the SLIGHTEST gasoline smell. Now, with the key on, engine off, the gauge first registered about 35 psi. I went ahead and started the car. The pressure shot up to 45 psi, and then dropped back down to a steady 40 psi at idle. I let the car sit and idle for a while and shut it off. The gauge remained right at 40 psi and I left it there for exactly 20 minutes. When I went back, the pressure had dropped to 32 psi. I held the purge button on my fuel pressure gauge and let it drain into a gas can until nothing more would come out and unhooked the gauge. I put the fuel rail covers back on and closed the hood.

Now here is where it gets good. I started the car, and I am telling you, it felt like I had just started a new Cadillac. I put the car in gear and I swear, I literally could not tell for sure if the engine was running. No throbbing. No bouncing. Nothing. Just smooth as glass. My 2000 Toyota Corolla doesn't idle this nice! The car had NEVER idled this nice since we got it, EVER. I drove around for about 10 minutes or so like this, with my jaw hanging open. I simply could not believe how smooth and responsive the car was. Every traffic light I came to, the car braked to a stop without any drama during downshifts, and settled right back into an almost imperceptible idle.

But of course, as it always is when troubleshooting a car, just when you think you've got a problem solved, it comes right back. As I said, within about 10 or 15 minutes of driving around, the idle began to creep back up, and a slight throb began to return. Within 20 minutes or so, once again, keeping the car still a traffic light required a bit more firmness against the brake pedal. Idle, in gear and stopped, was right between the 500 and 1,000 RPM hash marks on the tach and a bit "throbby". Not bad, but DEFINITELY not what it just was 10 or 15 minutes earlier. Another short drive this evening after the car had sat for about an hour, resulted in the lower "starving for fuel" idle issue at first, but by the time I was backing the car into the garage, I was needing a bit more brake pedal pressure, as the idle had climbed back up again.

So, is it possible that the unbelievably good idle that I had right after "burping" the fuel rails be a clue? Could air getting into the fuel lines somehow cause this kind of whacked out idle? Did the enormous pressure relief from unscrewing the gas cap have anything to do with this? If definitely made a difference right after I filled the tank and restarted the car, as it went from idling too high, to idling too low with doing nothing more than filling up the tank.

I'm thinking that my fuel pressure regulator might be on its' way out, but I've spent a LOT of money on this car since getting it, and the last thing I want to do right now is run off and blindly replace yet another part in hopes of getting this problem fixed. Is there anything else I can do to verify the FPR is going bad, or any other tests I can try to look for problems elsewhere in the system?

I can't help but feel that I'm THIS CLOSE to getting this figured out though!!

Thanks in advance for any input.

Ron

mseven

to me this would mean more tuning (ecm/chip tuning) is needed and compensation (adding fuel) to that side (140blm) is needed.
However, I would also be looking at the 02 activity, are the cross counts moving rather quickly or are they sitting at .450-.500 without movement, or moving slowly (you will want to look at what is going on for both banks), this will need to be viewed when warmed up , at operating temp., and in closed loop.
Either side may not be right, the 128blm does not ensure 02 is operating correctly, cross counts will be a better determining factor, and of course data logging to understand were the 140 blm (lean spot ) is happening (load vs rpm area).

this sounds as though in open loop all is fine until entering closed loop, where there is a fueling , and IAC count issue. Check to see if this happening when the car enters closed loop operation.

If testing with the vac disconnected I usually start with the pressure around 43.5-44 psi. From there if I smell or see fuel from the FPR vac line, that tells me there maybe an issue with the regulator. I would start by doing the normal FSM fpr regulator checks and tape the guage to the windshield to see what is happening to the pressure under load. Additionally setting the min. air using counts works the best for me to control idle. For a close to stock motor 10-20 counts, on a modded motor around 40 counts (using your scanner) in closed loop and at normal operating temp.

surfer92

Having a 92 and a 93 and 93 has Bosch III's, 92-93 ECM's does not handle mods well.
III's are 24 lb injectors and yours calls for 22 is your 1st problem.

2nd, sounds like you have a vacuum leak, I chased my tail trying to solve idle issue on the 93, finally replaced all hoses and rubber boots, including the PCV hoses and grommets.

Pressure at the tank, meant the Evap system is not working correctly and let me tell you, it is a MAJOR pain to get to the cannister.

Next, pull codes, there are several codes that will not trip the SES light.
If you have a Quad driver error(QDM 3) DTC 28, it is either a bad fan relay or more likely the Evap solenoid is bad, causing the pressure in the fuel tank.

Also, there are vacuum lines EVERYWHERE, so just don't look around the intake for leaks.

screamin_conure

Hey, thanks guys! Actually, according to the folks at FIC, the Bosch injectors that I bought are actuall 22# units specifically for my year of engine. I think you're on the right track with the EVAP system though. All of the web research that I've been doing today, along with the following blurb from the FSM, have me thinking I have an EVAP issue somewhere.

Here's the passage from page 6E3-C3-2: If the canister purge solenoid is open, or is not receiving power, the canister can purge to the intake manifold at the incorrect time. This can allow extra fuel during warm-up, which can cause rough or unstable idle.

I had the revelation late last night that when I had the passenger side fuel rail cover removed, something didn't look quite right on that side of the intake manifold. As soon as I get home tonight, I'm going to give the canister purge vacuum solenoid a look. I think there might be something disconnected there. Does this solenoid have its' own vacuum connection into the intake manifold, or does it share manifold vacuum from the small cluster that is attached to one of the two nipples on that side of the intake manifold (the other being the connection for the fuel pressure regulator)?

jaa1992

IIRC it gets the vaccum from the TB.

I still need to trouble shoot mine cause I get a lot of pressure build up in the tank. I have a new hose from the TB and a new selenoid. Its probably the expletive deleted canister or lines to it.

surfer92

According to Bosch, there is no 22# inj, I think Jon tries to tailor the FI's to 22, from 24, not putting Jon down, but I think that is a iffy way to go. Unfortunately, Multitec's are the only other way and rebuilt ones run $280+ for a set and new are around $6-700.

The solenoid sits right beside the TB, in the valley between the intake and the heads.
Do not just assume the solenoid, check the hoses. I had several bad, both upfront and back at the canister, canister is tucked in the right quarter panel and is a MAJOR pain, also check the canister filter, mine was gone after 16+ years.

GlennS87

What are your IAC counts at idle? I would guess it's a vacuum leak based the BLM's. If you're IAC is acting erratically this would cause your poor idle. When you replaced the IAC did you do the reset procedure that allows it to position itself properly. (the procedure escapes me at the moment but I'm sure it's somewhere on the forum.

screamin_conure

IAC counts at idle seemed to vary. At times, usually when it was idling high, they would be zero indicating that the IAC wasn't able to compensate for whatever was driving up the idle. Usually, they were around 20 - 40. And yes, I've done the IAC reset procedure several times (hold down accelerator slightly and start engine, let run 5 seconds, shut off, let sit 10 seconds, restart).

I checked out the canister purge solenoid yesterday and all looks good. I applied 10" of vacuum to the throttle body side with a hand vacuum pump and it held just fine. I then jumpered pins A and B on the ALDL connector and turned the key on (no engine start) and the vacuum on the purge solenoid dropped right down to zero the instant I hit the key, so that tells me that the solenoid should be good.

Yeah, it's definitely getting some false air from SOMEWHERE but I just can't seem to figure out where. My mechanic ran smoke through the system last year and couldn't find anything. I have a can of TB cleaner, so maybe this weekend I'll try hitting it with a squirt here and there to see if I can detect anything. I'm going to try to do some further testing on the fuel pressure regulator as well.

Thanks again for all of your suggestions guys!

Ron