87 16V running rough

Have an 87 16V that started running very rough when driving in town. Runs rough at all rpms. Checked wires, plugs, cap and rotor and are all OK. Smells like the fuel to air mixture is very rich.

Any ideas.

Wayne

Reply to
Wayne Faas
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Assuming its really running very rich (and it should be noticable in your gas mileage). It's most likely a bad O2 sensor, coolant temperature sensor, or stuck air flow meter. First thing I'd do is check the differential pressure regulator current, it should be bouncing around a little, but never get far from 8mA or so. If its constantly high I'd check your CTS then your O2 sensor. If its not moving at all, your O2 sensor is probably bad and its out of adjustment.

Reply to
blah

I too have an 87 GTI 16V that I just picked up a few months ago and mine is doing the same. It REALLY runs rough when you first crank it and then it is noticeably rough at idle but seems to do okay when you are at highway speeds. It was running VERY rich so I leaned it out with the air bypass screw but that still didn't do anything for how it ran. What is a "CTS"? I have a Bentley book but I don't know what a CTS is?

At least I am not alone on this problem..

Any help would be appreciated.

Dave

Reply to
David Craig

I too have an 87 GTI 16V that I just picked up a few months ago and mine is doing the same. It REALLY runs rough when you first crank it and then it is noticeably rough at idle but seems to do okay when you are at highway speeds. It was running VERY rich so I leaned it out with the air bypass screw but that still didn't do anything for how it ran. What is a "CTS"? I have a Bentley book but I don't know what a CTS is?

At least I am not alone on this problem..

Any help would be appreciated.

OH, I checked all the same stough that he did....plugs wires cap...etc

Dave

Reply to
David Craig

CTS = Coolant Temperature Sensor.

Reply to
Matt B.
87 16V running roughOn my '89, I've had lots of O2 sensor issues. Mine used to run a bit rich on startup, then would lean out after warm up. I had a cracked downpipe, and I don't know if that affected things by allowing a blast of outside air to come in. Anyway, I finally addressed the problem when, during very wet weather or snow, the car wouldn't rev up over idle. I resoldered the wires and heat-shrinked the connection and that helped the major problem. If a little water gets in there, it will never get out.

On mine there's an electrical connection near the firewall, under the hood, on the passengers side, from the oxygen sensor. I used to unplug that when the car was running too rough to drive, and the car would then smooth out because the shorted out oxygen sensor was out of the loop. You could try unplugging the O2 sensor at that location and see if, after a few seconds, it smooths out. If so, you know where the problem originates.

Another time I had rough idle, and I did all the differential pressure regulator current tests etc., and everything was fine. I then cleaned the round shiny air intake plate. It was sticking (it should lift up easily and Germanically smoothly) until I cleaned some oil and gunk off it. That helped a great deal. That plate is discussed in the Bentley manual. For some reason I'm blacking out on the exact way to access it, or what it's called... I'll get back to you.

There's always the dreaded idle air stabilizer valve... someone once told me to tap it with a hammer to see if that clears up rough idle, but it never seemed to.

As others have said, the coolant temp and thermo-time switches could cause rich running. Disconnect the wires to those things and check the connections and wires. I recently had to re-solder the wires to the coolant temp sensor. Corrosion and heat damage to insulation are common. Bad CTS wires or sensor itself, on my car, caused very difficult cold starts, but did not affect running once the car was started and warmed up.

I'll peek under the hood of mine and break out the Bentley to jog my memory.

Any ideas.

Wayne

Reply to
Theo

If you have to do this, make sure to stagger the cuts and as Theo said, use heatshrink, not electrical tape. Cracked exhausts have a habit of making O2 sensors read incorrect values, so make sure the exhaust is in good shape before assuming a problem is related to the O2 sensor. Also, the O2 sensor will have no impact on the performance of the car for the first 90 seconds or so of operation.

Contrary to many peoples' beliefs, unplugging the oxygen sensor will not cause it to go into limp home mode, it will simply ignore the oxygen sensor. So Theo is correct, you can always try unplugging the O2 sensor.

There's a rubber boot with a large hose clamp, just loosen the hose clamp and remove the boot. Lift the plate with a magnetic pick-up tool. It should move easily and smoothly. If not, clean it, if it still doesn't, try to fix it, but most likely you are looking at getting a new (used) one

-- you don't want to know how much they cost new.

It amazes me how much people like to blame the idle stabalizer valve for all their maladies. I'm not saying they never have problems, but I think its heavily misdiagnosed. If you suspect the idle stabalizer valve, first thing to do is unplug it and see what happens. If there is no real change then its probably not the ISV. If there is, remove the ISV and clean it, then try again. The flapper should move easily, and when released from an open position return to an almost shut position. If nothing has changed, the first thing to do is suspect an air leak. Primary air leak sources are the fuel injector seals, and any vacuum lines or rubber boots. All lines and boots must be crack free, and tightly sealed. Loose hose clamps are unacceptable. Try spraying ether (car starting fluid) anywhere that is suspect. Also try squeezing rubber boots. If the idle changes, even slightly as a reaction to any of this, there is a leak. An air leak can easily cause a perfectly functioning ISV to create a hideously unstable idle.

On CIS-E cars the thermotime switch is *ONLY* used to aid in starting the car when cold. The operative word here is "STARTING". Once the you are no longer cranking the start, the thermotime switch is completely out of the picture. In order to have a failed thermotime switch affect a car while running, you would also have to have a faulty ignition switch and wiring simultaneously. A faulty CTS could absolutely cause problems. Its just a resistor with a temperature coefficient, so its trivial to test (just measure the resistance when warm and cold and compare to the chart in the Bentley.

Reply to
blah

Theo and Blah,

Thank you so very much for your input. I value each posting and will put your advice to good use.

Thank you again,

Dave

Reply to
David Craig

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