Engine lopes

morbid · 12-13-2006, 06:46 PM

Another problem with my car, again... Now the engine, fuel injection, or vacuum system is sick. Engine started to lopes while idling, and stalls when I hold accelerator steady. Some times when it stalls it keeps missing until turns off, and it's hard to start, hot and/or cold. What can it be? Some vacuum leak in fuel injection system, auxiliary air valve, electrical...? I put on a fuel pressure gauge and the system maintains the fuel pressure even when the problem appears, so lack of fuel and/or fuel pump is not the problem. This night I tried another flow meter and DME with no luck.

Thanks in advance...

JivenJim · 12-14-2006, 12:12 PM

I'm thinking Bad throttle postion Sensor or Air flow meter.

check http://www.clarks-garage.com/index.htm
ELECT-19, Sensors and Gauges - Information, Troubleshooting, and Testing

Good luck

Razorback1980 · Razorback1980's Garage

Sounds like a vacuum leak somewhere to me. Check to make sure all hoses are connected to the J boot securely including the one on the underneath side at the corner and also check the other fittings around the intake manifold.

morbid · 03:23 PM

For me the TPS don't do that but, the air flow meter. I tried with two AFM I have with no luck. Will test with another ignition coil, and auxiliary air valve.

Will check Clark's Garage...

Thank you guys

ERAU944 · ERAU944's Garage

when i put a flowmaster on my car, and only the flowmaster, i had a bit of loping... is it less than 50 rpm difference? if so, my bet is that it's the lack of back-pressure... after i switched back to the stock muffler, the loping went away.

morbid · 12-14-2006, 07:01 PM

Quote:

Originally posted by ERAU944
when i put a flowmaster on my car, and only the flowmaster, i had a bit of loping... is it less than 50 rpm difference? if so, my bet is that it's the lack of back-pressure... after i switched back to the stock muffler, the loping went away.

Let explain me better. My car was running great with its Flowmaster over years, and two day ago while engine's idling it started to lopes frequently, like it's at 1,000 rpm, goes 500, and returns to 1,000, on and on. Now, you start the car, let it idling at 1,000 rpm, and in a minute it starts to drop to 500, and up to 1,000, on and on, and on...

ERAU944 · ERAU944's Garage

ahh, yeah that's a bit much. does it seem rich or lean at idle? is the problem only at idle? does the car run normally off idle? could be a faulty fuel pressure regulator, a clogged fuel filter... i'm thinking fuel related here

JivenJim · 12-15-2006, 11:09 AM

Sounds like Idle control Valve. Had same problem in my Honda.
First try bleeder screw on water return on head with engine warm and heater on full. Air Bubbles can cause problems. If no luck there, I'd buy this.
http://www.*****************.com/product_p/pp930.606.161.00.htm

morbid · 12-15-2006, 06:11 PM

Quote:

Originally posted by ERAU944
ahh, yeah that's a bit much. does it seem rich or lean at idle? is the problem only at idle? does the car run normally off idle? could be a faulty fuel pressure regulator, a clogged fuel filter... i'm thinking fuel related here

For example: today I started the engine for the first time this day. I let it idling (at 1,000 rpm), when the car is reaching normal working temperature it started to drop the rpm (lopes from 1,000 to 500 rpm)) every 30 seconds for a minute or two. Then the frequency of the lopes started to be in shorter time lapses, until the engine lopes continuously. I let the engine loping for a little more time , it started to miss without loping, keeping at 500 rpm (more or less), until the engine turned off. I started it again and now it can't be accelerate normally without turning off, it just cranks without started. This was done with a fuel pressure gauge on, showing no fuel pressure drops, assuming fuel delivery it's ok. The injector plug was tested with a noid light and pulses are ok, assuming injector pulses (DME) Ok. What I noticed today was spark-plugs sparks sometimes wont appeared (with a new coil and two DME tested). Flywheel sensors?... Fuel pump relay? Bad relay ground? This thing is bothering me since this summer... The problem appeared last two weeks of June, disappeared first week of July, and appeared again last Monday...

ERAU944 · ERAU944's Garage

ahh only does it when warm - that possibly makes it a temp sensor.

anyone else have issues like this when they had a faulty temp sensor?

after reading a bit more i think you might be on the right track with speed/ref sensors. my friend was having problems with his 951 intermittently running like garbage, and it turned out to be a bad speed/ref sensor.

anyone got any other advice to offer?

Taz's Master · 12-16-2006, 04:58 AM

My problem with a bad speed/ref sensor was a no start condition when warm. No drivability issues when running. Also, the fuel milage gauge wouldn't move when the sensor was giving me trouble.

ae1969 · 12-16-2006, 06:21 AM

FYI possible causes of a hunting idle, vacuum leak, o2 sensor, idle stabilizing valve, TPS, blown engine

.......What you describe..........a hunting idle like that usually indicates a vacuum leak after the throttle body. I would venture that it is more than likely one of the hoses under the intake manifold. The hunting is caused by the DME attempting to adjust fuel for the extra air.

When you disconnect the O2, it forces the DME into open-loop mode so it just uses a sraight look-up table rather than relying on O2-sensor feedback.

So unplug the O2.......... It should level out. I would spec out the sensor as well.

morbid · 06:47 PM

I see my friends... I'll look for the vacuum hoses under intake tomorrow, change the coolant temp sensor, clean the auxiliary air valve, change the idle air valve, and look the flywheel sensors. Will do all that bunch at once. What ever is disturbing should disappear... (I hope). Took a ride today to my work, and another to come back home. Need the car so bad, and don't have time to diagnose part by part. I wonder what SoCallDriver can tell about.

morbid · 06:53 PM

...My car is haunted... Changed all stuff I said I'll change today, engine cranks but no start. No volts to fuel pump but sparks at plugs and pulse at injectors, so engine wont start. I jumped between fuses #2 and #3 like I did before to run the car, but it wont run. I took off the jump, cranked and engine ran until fuel pressure drops. With ignition switch off, I jumped by hand again for few seconds to charge fuel, took it off, cranked again and engine ran. But when I jumped fuses with engine running, it instantly turned the engine off, like some kind of short...

Mmmm... Another ride to work tomorrow...

dally_de · 12-25-2006, 10:02 AM

i had the same problem...and it was from throttle position switch.

morbid · 12-25-2006, 07:51 PM

You know? There was no short, nor TPS, Air Flow Meter, DME... My car is ok by now. I fixed yesterday. The problem was too much fuel, or an over riched mixture. That was why the engine missed through shut off when the pump was on, and runs well while the fuel pressure was about 10 psi and down. Want to know what I found while I was going to measure the coolant temperature sensor?

This car ('84) has a 1k Ohm resistor soldered in the yellow wire right before the plug that connects to the temp sensor... the resistor was broken. I still have the DME/Sensors wire pack from my '83 944, and this is not presented at the coolant temp sensor plug. Is this normal with this two year 944 models? Anyway...

I went to the nearest Radio Shack, bought a pack of 5 1k Ohm resistors for $1.09, soldered a new one where the other was, fastened the plug, put in the fuel pump/DME relay, the fuel pump fuse, cranked the engine... and the "lovely" engine ran better than before at idle and at high RPM from cold to normal temp.

The whole problem was that broken resistor. And the car was parked for more than a week for that... Jesus Christ!!!...

Thanks a lot for your input in this matter people.

338WIN · 10-22-2009, 12:27 PM

Sorry about starting up an old thread, BUT I might have the same issue and have a question.
I have an early '83 that I finally got back on the road. It is loping at idel every second or two within a minute or two after it is running.
I'm glad this seems to be the only problem so far.
Do I need to cut the wire wrap to see if I have a resistor inline? If I don't sounds like I should replace the temp sensor and the O2 sensor and expect to eliminate the trouble?
Great to be on the road again. Fixed a bent valve from the PO and replaced the rubber dampner (automatic.) I'm certainly not an expert but have become intimate with a lot of the car!

morbid · 10-22-2009, 09:05 PM

I remember an early '83 I had before the '84 I have now. And when that problem appeared in the '83, I just replaced the auxiliary air valve and problem was resolved. I thought the same when the problem started with the '84 I have now; but as you can see above, it took too much to got over it...

You may check the auxiliary air valve first, then if there is any vacuum leak in the intake... The next steps are already explained in the thread.

Good Luck!

338WIN · 10-22-2009, 09:09 PM

Thanks morbid,

I'll do just that.

It is good to be rolling low again.

I've got a 1980 Yamaha xs1100 parked next to the 944 and I noticed this morning that my head is about the height of the motorcycle seat!