Very bad idling after cold startup

[max517]

The car is a 1992 Plymouth Laser AWD 5 speed. No mods, everything is stock. 114,000 miles.

Problem:
The car always starts up easy, but then immediately drops down to low rpms, probably about 500-700, and shudders there for a couple seconds, then comes back to a smooth idle at around 900-1000. However, if I press down on the gas peddle just the littlest bit (I'm guessing just enough for the engine to be off the idle circuit), the RPMs decrease again and the car shudders again. It then returns to normal after letting off the gas completely. Anytime after being revved, either in neutral or in gear, when it drops back to idle the revs fall real low and it shudders for a second before the idle raises again.

Other information:
It ONLY does this while cold. By the time the temperature gauge is passed the first line, it idles very solidly at probably 900-1000 rpm. I can press on the gas peddle just the littlest bit just like when its cold, and the RPMs increase a little as they should, instead of dropping.

One day (a while ago) it just wouldn't idle at all, immediately dying after starting uneless I'd give it gas. After a long time of running, it would eventually idle very very poorly. Changing the fuel filter helped, and it would idle on its own (how it currently does).

I have checked for boost leaks using a boost leak tester (http://www.vfaq.com/mods/ICtester.html) and also by spraying starting fluid. I found a leak however fixing it made almost no difference.
I checked the resistance on the ISC terminals with a multimeter and they were all good.

I've searched a lot and am stumped as to what to try next. Have any ideas?

Within the next few days I will hopefully have a PDA with MMCD (the free datalogging software) to play with, and assuming I figure out how to use it, is there anything I should check with that?

Thanks and I greatly appreciate any help

 

[98RedDragon]

that hapened to me in my old 97 eclipse RS, when i started it in the winter sometimes the computer would get stuck in the "cold start" mode and sometimes it would even die, i would turn it off and on and it would work again. it sounds like the same thing, except that yours has a turbo. eventualy i replaced the ecu for numerous reasons and it never happened again.

 

[brn2race96]

it might have to do with the coolant sensor, or even you fuel pressure regulator.

 

[max517]

Try adjusting the biss screw located on the throttle body next time you start it up, turning it counter clockwise to open up more air for the car, and clock wise to lower air.

Do you have coolant lines running into the throttle body ?
If not the FIAV is not working correctly and making cold startups a pain.

I tried the biss screw, turning it counterclockwise. It still stumbled down to low rpms just the same, the only difference was once the idle steadied itself out, it was a little higher than it was before, like maybe 1100 rpm. Still, putting my foot very lightly on the gas would drop the rpms etc.

I have the coolant line. My only question is would possibly having a stuck open thermostat or no thermostat cause the coolant to not go the FIAV?

that hapened to me in my old 97 eclipse RS, when i started it in the winter sometimes the computer would get stuck in the "cold start" mode and sometimes it would even die, i would turn it off and on and it would work again. it sounds like the same thing, except that yours has a turbo. eventualy i replaced the ecu for numerous reasons and it never happened again.

This happens everytime, I can turn it on and off and it will always have the same symptoms.

it might have to do with the coolant sensor, or even you fuel pressure regulator.

My temperature gauge works and the fans come on at the correct time, is it still a possibility a coolant sensor isn't working? How would I check the fuel pressure regulator, and would it make sense that the problem goes away once I reach operating temperatue?


Also, I now have a working logger setup, running MMCD on a pda. Although it is pretty cool, I don't think I've found any problems with it. Just to make sure though, is it normal for the ISC reading to stay the same? If there is anything else I could check for abnormality with MMCD, I can now do that..

Thanks

 

[Jimmy Jr.]

The biss is a constant regardless of cold start or operating temp so if the car runs correctly in one scenario and not in the other it's not the constant, aka biss. It's not the coolant temp sensor nor is it the fuel pressure regulator. Try cleaning your tb and see if that helps any. A new o2 sensor couldn't hurt.

 

[ddavisaf]

You need to do a boost leak test.
Then check your ISC.

Forget everything else. Check for a boost leak. Then check your ISC.

 

[max517]

with your logger, make some logs of your 3 fuel trims, monitor your coolant temp, and your o2 values.

And the biss is not a constant, it would if your isc was steady or blocked off. adjusting the biss gives more adjustment for the isc range, higher or lower within the same range of its own mechanical opperation, if you understand that.

If your o2 isn't cycling after your car gets warmed up, or reads really lame values like .01 or 3.+ its a goner.

If your coolant temp never changes, its toast. And just so you know the gauge is seperate from the coolant values the ecu has, the ecu uses the bigger 2 prong coolant sensor on the elbow.

Fuel trims are just for shits and giggles.

O2 sensor seems to work properly. Coolant temperature changes on the logger as well as the gauge in the car. Also the fans come on, so I assume its working properly.

You need to do a boost leak test.
Then check your ISC.

Forget everything else. Check for a boost leak. Then check your ISC.

I did another boost leak, and unless my testing thing really sucks, I'm pretty sure I have no leaks.

New thing I noticed:
It's almost impossible to hear with the hood closed, but when my key is in the on position the ISC clicks nonstop. With the hood open its pretty loud, it sounds sort of like an electrical short and electricitity is arcing or something, but its definately the ISC. When I unplug the connection it goes away completely. I'm wondering if its normal for it to click, constantly, or if that means its broken.

 

[arash15]

dsms are notorious for idle surge. make sure you check all your vacuum lines.

 

[max517]

You might wanna unplug your isc motor and test its coils. But it doens't seem right if your problems are only on cold starts.

Then again it is a dsm, practically a magical being from a universe long far away. Where your starter dies and now your mpi fuse blows.

I tested the resistance between the terminals and they were all within range. I didn't try applying voltage to them (didn't have the supplies) but since its clicking I assume its doing something. I'm just wondering if its normal for it to click forever with the key in the on position, or if that means its stuck or something..

 

[ddavisaf]

Start your car. Wait for the surge. Unplug your ISC. If the problem goes away it's your ISC.

If it were fuel related you'd be able to tell real quick. If you're running rich at idle you'll smell it and your o2 would have a shit fit. If you're running lean your o2 will have a shit fit.

Since your o2 voltages seem to check out fine I doubt it's related to that.

What I DO suspect is your..... ISC.

Take it out. Clean it up. Then try my little test ^^^^.

If you'd like me to find the vfaq related to this problem let me know and I'll happily send it over to ya.

 

[max517]

Start your car. Wait for the surge. Unplug your ISC. If the problem goes away it's your ISC.

If it were fuel related you'd be able to tell real quick. If you're running rich at idle you'll smell it and your o2 would have a shit fit. If you're running lean your o2 will have a shit fit.

Since your o2 voltages seem to check out fine I doubt it's related to that.

What I DO suspect is your..... ISC.

Take it out. Clean it up. Then try my little test ^^^^.

If you'd like me to find the vfaq related to this problem let me know and I'll happily send it over to ya.

My o2 stays really low, like .01-.03 until it warms up, then it moves around a lot. Is that normal?
I tried what you suggested, starting the car with the ISC unplugged. It didn't make the problem go away, however it ran EXACTLY the same as when it was plugged in. Am I wrong in concluding that this means the ISC isn't doing anything and is therefore broken? Wouldn't you normally notice a difference if you unplugged your ISC?
I took the ISC out, and apart earlier and it looked really clean. I used some carburator cleaner to clean it even more, but no difference at all.

 

[ddavisaf]

No no, start the car. Wait two minutes then unplug the ISC.

 

[scrim016]

I have a 97 Eclipse GS with a stage 2 setup, whole different engine but the exact same problem. Only happens on cold starts, once engine seems to be warm idle is normal again. Do you think its anything to do with the 02 sensor behind the cat since i did clean out the cat. I replaced the ECU and it ran good for the first ride. On second start a day later it ran liek shit again and would stall out upon starting without alitle throttle. Anyone know anything knew?

 

[max517]

Well hakcenter solved the (specific) problem...
It was leaking throttlebody shaft seals. However, after replacing those, I have yet another idle problem. This is now the more common surging over 1000 rpm. I tried moving the BISS, and didn't get any luck with that. I'm pretty sure its the ISC, I'm just looking for verification. When the key is in the on position, a constant very loud clicking comes from the ISC. I'm fairly certain it didn't always do this. I pulled the ISC out and put the key in the on position, and the clicking sounds way louder, the whole thing constantly vibrates sort of, and the shaft part of it twists barely at all back and forth. The tip was a little dirty, but inside it was very clean and spun really smoothly. As I said earlier, the resistances were all good. Is the ISC good or bad. Any ideas?

Thanks

edit:
after driving it more, the idle is totally erratic maybe not even better. I'll start it up and it idles perfectly smooth at 1000, i touch the throttle and it starts surging between 600-1000... sometimes it idles at 1300 or so. Turning on the AC either does nothing or drops the idle. Who knows.