Hello Everyone. Can’t tell you all how grateful I am to have a resource to reach out to for help with my van. Haven’t had any luck so far finding a local service center that is willing to work on it. This is my first ever post to any kind of forum so if I am not doing this correctly, or not in the correct place on your site, please let me know.
I have a 1987 automatic with about 270k miles on it. Drove it as my daily driver for the last 7 years but it is now out of service and I have been thus far unsuccessful at resolving the problem. My skill set for carrying out repairs on vehicles is overall good, but my diagnostic skills are limited, which is what brings me here.
The situation began as what I think would be described as a “misfire” by most technicians, but that might not be what is actually occurring. These hesitations when driving were intermittent and the duration was only a split-second. During that split-second, the Check Engine light would come on and off one time in unison with the hesitation, and it felt as if something has suddenly interrupted the fuel or ignition.
Another odd thing that was happening was that, with the transmission in Park, with engine running, and applying enough throttle to hold at about 2,000 RPM, the engine RPM’s started fluctuating up to about 2,200 RPM, then dropped back to 2,000 RPM, then repeated this cycle continually – even though I was not moving the accelerator pedal (I was holding it steady). Similarly, another thing would occur…with the engine at full operating temperature, transmission in Park, and idle engine speed, exactly every 10 seconds the engine RPM would drop down about 200 RPM, stay there for about 1 second, then return to normal idle. This cycle repeated itself constantly.
A diagnostic code indicative of the TPS circuit showed up. I replaced the TPS itself, then cleared the code and it has not returned since then (also, the old TPS had something rattling around inside it so I assume it was indeed needing replacement).
After replacing the TPS, the hesitation issue continued and increased in frequency and intensity until I had to stop driving the vehicle. It then became very stubborn to start (cranked fine but would struggle to start and have a very rough (stumbling) idle at first, which required me to rapidly & partially pump the throttle to keep it from stalling out). If I managed to prevent it from stalling, in a few seconds the rough idle would correct itself and engine operation would seem normal for the moment.
However, before I was comfortable road testing it, I decided to increase the throttle and hold it at 2,000 RPM for a bit and observe the behavior, and about 2 seconds after holding steady at 2,000 RPM, the Check Engine light came on and the engine stalled out, and refused to crank again. I immediately checked for any codes but there were none being reported.
Next, when the engine was cold, I cranked it and let it run at idle RPM to see if it would keep running, but after about 10 minutes, the same stall occurred. Then, I noticed something new happening just after the stall occurs, when the ignition switch is still on but the engine is no longer running due to the stall, the Idle Speed Control VSV was making a loud rapid clicking sound, which I assume was the valve itself opening and closing. VERY strange. I removed this VSV and bench tested it per the instructions in the FSM and it passed all of it’s tests.
Next, I verified power to the spark plugs (by pulling a plug wire, placing a screwdriver up into the boot and holding the screwdriver near the block while bumping the ignition switch to see if electricity arcs between the screwdriver & engine block), and they all seemed okay BUT I decided to replace the spark plug wires anyway (the spark plugs themselves have only about 6,000 miles and were installed 2 years ago). After replacing the spark plug wires, the engine will crank immediately but the idle RPM’s still fluctuate slightly (drops by about 100 RPM, then returns to normal, about every 2 seconds, continually).
I have noticed that after the engine stalls out, the next day it will usually crank immediately on the first try but will not remain running for long before it stalls again, especially if I put the transmission into gear and attempt to drive it even a few feet. It might remain running until I can get it parked better in the garage, if I’m lucky – but then stall out again.
Finally, the last thing I noticed is that now (with engine running) suddenly the AC compressor will not kick on when I turn on the AC switch.
Thus far, using the test procedures described in the FSM (for what that’s worth, and also just a side note, I am using a 1989 FSM, so I hope that’s okay), I have tested and ruled out the following components:
Primary Coil
Secondary Coil
Igniter
Fuel Pump
Idle Speed Control VSV
In addition, the distributor cap interior rotor button contacts were cleaned by scraping off some of that white residue that forms on them, using a dental scaler.
Spark plugs seem to be in good condition.
Spark Plug wires are brand new.
I would very much appreciate any guidance on how to resolve this issue. Thank you so much!