Low idle

darisb · 01-18-2003, 12:54 PM

Pulling the '74 2.0 out of storage.

I installed a rebuilt fuel pump, replaced the fuel filter, replaced the fuel strainer in the tank, all the fuel hoses, and set the fuel pressure at 29 lbs. (engine not running).

Replaced the intake manifold gaskets and boots. Cleaned and checked the injectors. None are leaking, and all are spraying when I turn the engine over. Replaced the large and small injector seals when I reinstalled them.

I verified that all the hoses are connected properly. And, I cleaned the throttle body, and replaced the gasket under it. I even removed the air filter element on the last run.

The car will only idle around 600 rpms, with the idle adjustment screw backed all the way out on the throttle body. The car runs pretty good at speeds, but will burp sometimes when I let off the throttle on a hard acceleration.

Any suggestions?

Bruce Allert · 01-18-2003, 01:32 PM

How about checking dwell & timing. If it isn't timed right you can get either a fast or too slow idle. Is the burp a kind of backfire? It could also be running too lean. Try bumping the adjustment on the ECU clockwise 1 to 2 clicks after checking dwell & timing.
bruce

darisb · 01-18-2003, 01:51 PM

Thanks Bruce. The burp is a soft back fire. I was thinking about the timing and the valves after I wrote the original post. I'll have to pick up some valve cover gaskets and make those adjustments next weekend. The ECU us currently adjusted all the way clockwise.

hardflex · 01-18-2003, 02:06 PM

does the idle come up if you disconnect the vacuum line from the distributor? sure seems like if you let the air in the engine speed would come up.

darisb · 01-18-2003, 03:08 PM

Thanks hardflex, I'll give that a try next weekend.

John Rogers · 01-18-2003, 04:25 PM

You might want to check the fuel pressure with the engine running. Sounds like the pressure might be too low? Good luck.

darisb · 01-18-2003, 04:38 PM

The Hayes manual states that the pressure should be between 28.4 and 29.6 ft./lbs. I set mine to 29 ft./lbs. Is that the same pressure that it should be at when the engine is running?

HMeeder · HMeeder's Garage

It may be the same, but the 29 lbs is the constant pressure and what the system needs as fuel is being drawn out by the injectors. I always check it while the car is running.

Truthfully, sounds more like a timing issue to me. Valves probably wouldn't do it unless they are waaaay out. (Don't need valve cover gaskets to do a quick check on that!) If you still have points, they may have slipped or more likely, corroded a bit affecting the dwell. This will in turn affect the timing. How does it feel when you are driving? Got full power under acceleration or does it seem to "lag" a bit?

pbanders · pbanders's Garage

From what you've said, I suspect your ECU idle adjustment knob is set very lean. When the idle mixture is really lean, adding additional air (opening the bleed screw) has no effect on idle speed. Additionally, you'll get backfiring when the throttle is closed, because the ECU sets the mixture to the idle mixture condition when the throttle is closed. I would suggest turning the ECU knob at least 3 or 4 clicks clockwise to richen the mixture.

Your fuel pressure is fine. As HMeeder says, valves must be adjusted to spec and ignition system must be in perfect working order, among other things.

darisb · 01-18-2003, 09:21 PM

Stumbles at the low end, but seems to have full power at speed. I've got electronic ignition in it. If I remember right (it's been in storage for three plus years), it ran like that before I installed the electronic ignition. I was hoping that the electronic ignition would cure the problem, but it didn't.

Perhaps I haven't been setting the timing correctly fromt the beginning. I never had any trouble with my previous 1.7. I'll have to take another look at the Hayes manual, and give it another try.

darisb · 09:25 PM

Mixture knob on the ECU is all the way clockwise.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

A rich mixture can also cause the idle to "sag" down, and the throttle's idle bypass screw will have very little effect on it. You might try leaning the knob on the ECU and see what effect that has.

Timing is another suspect.

Then again, the last time my motor did this, it turned out an intake valve was no longer sealing, allowing the intake charge to get pushed back into the intake manifold, increasing the pressure there... So the FI simply put more fuel in.

Oh, and the valve wasn't sealing because the seat had dropped. Again. Do a compression check to make sure that you don't have this kind of problem. (A "poor man's compression test" can also tell you--does the starter crank evenly, or is there a "drop out" in the cranking noise??)

--DD

pbanders · pbanders's Garage

Like DD says, it can also be the other extreme, too rich at idle.

It is extremely difficult to do good troubleshooting by remote control (aka: through this forum)! Depending on where you're located, there may be a list member who is local and knowledgeable of the FI system that can help you.

darisb · 01-21-2003, 12:49 PM

I think I'm going to go through the car again. I used to work on 914's all the time. It's been about four years since I've worked on one. I want to go through the car first and make sure that everything is right.

It's very possible that the timing is off. The car runs good at speeds, but not very good at idle. Looking at the Hayes manual, it's possible that I glanced at the time diagram and set the timing at TDC instead of 27 degrees BTDC. That would explain why it stumbles at idle, but runs fairly well at speed. And, also would explain the low idle.

I also noticed that the exhaust valves on a 2.0 should be .008". It's also possible that I set them to .006" like I used to do on my 1.7 (and my aircooled VW's). Heck, anything could have happened four years ago.

That got me to thinking that checking all the settings on the car would be time well spent.

My problem is I'm not supposed to work on my car where I live, and the cranky old guy that lives next door loves to call the property managers on people. Luckily for me, he's gone every Saturday from 8:00 AM to 1:00 PM. Guess where I will be Saturday morning?

darisb · 01-25-2003, 12:13 PM

Thanks to everyone that responded to my post! My car is running a little better today. I checked the valves, and sure enough the exhaust were set to .006 in. I also discovered that the timing was off a little. I bumped it up a couple degrees. Finally I turned the mixture knob back six or eight clicks and was able to adjust the idle to 1000 rpms. I definitely need an aux. air regulator.