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This is a continuing effort to get my newly aquired red 91 245 runing right. I got the car on ebay a few days ago from a Goodwill store in Indiana (200 miles from me). It has 230K verifyable miles. I first replaced a bad AMM (car will not stay idle after a few minutes of running). I can tell that it's running rich (slight popping from the exhaust). I first thought that the O2 sensor need to be replaced. After careful examining the sensor, it looks like it's good compared to a brand new one. As the car idles or runs, the O2 sensor output stays constant at ~0.5V. I checked the ECU and surprised to see that it has a 951 unit (looks like she already went through her original one). Upon replacing it with a known good 951, the O2 output signal immediately start to cycle between 0.1 and 0.85V. Also the idle speed came down closer to normal (0.9 compared to 1000 before the change). It idles and runs very smoothly now, only hope to get the idle down to close to 750 rpm.
I took the entire intake out this afternoon and scrub cleaned everything on that side. I'm pretty happy how far I already got with her. I'm sure one day I'll get the idle right. Thanks for reading. Erwin
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Did you clean the Idle Control Valve located just under the Intake ?
They get a bit gummed up and get sticky.
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.no.net/ebrox/Tony's%20cars.htm
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Hi Erwin,
It sounds to me like you're on the right path to get that idle correct. It is a fine adjustment between where the throttle plate sticks and where it is open too far to allow the idle motor control of the air flow. This gets to be a smaller, and finer, adjustment as the parts wear, but that thorough cleaning you're giving it will make it easier.
You're right to be surprised about the 951 behavior. The steady 0.5V reading is not typical of an ECU problem. It points to an open circuit toward the oxygen sensor, or broken (or cold) sensor itself, because the steady 0.5V is provided by the ECU.
Also, as you don't mention first trying a reset, (lifting fuse 6) I wonder if the first ECU had a limp-home setting stored in before you swapped it out.
When you get your idle all squared away, consider re-testing the other 951 to see if the results are the same as before. You might still have a good spare on your hands. Be sure the O2 sensor is heating. That voltage comes from fuse #4.
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Art Benstein near Baltimore
Santa Claus has the right idea. Visit people only once a year. - Victor Borge
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Hi, Art. I still did not have a chance to mess with the higher idle yet. However, I did find out what’s wrong (or NOT wrong with the 951 ECU). It looks like that at the time I did the previous test, I wasn’t patient enough to let the engine warm up well. After it’s completely warmed up, the O2 output starts to behave. Thanks for your advice. I could’ve thrown out a perfectly good 951.
Since the O2 ready looks good, I now suspect that the popping sound is not a sign of richer running, rather exhaust rattling. I’ll look into it later. Erwin
Tony, I did clean the IAV really well when I did the TB and intake.
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Hi Erwin,
Gee, it shouldn't take patience to get that oxygen sensor warmed. It should heat itself up in a minute or maybe even less. That's why I think you might want to check the heater.
Two things could go wrong. The heater in the sensor could die, or you could be missing power to it. The power comes from fuse 4, which also powers the tank pump, so check that first. You might just need to spin the fuse. The best way to check is leave the fuse alone, and check for power at the sensor's connector, the two-pin socket where the white wires from the sensor tie in. That way, if there is power, it isn't because you disturbed the fuse.
If there's power there, you can check the heater by first plugging it back in, waiting a minute, then with your ohmmeter ready in quick-draw style, pull the plug apart again and measure the resistance toward the sensor's heater (the two white wires). A good heater will show you a declining resistance value from maybe 12-15 ohms warm to something like 4-5 ohms cold. All you really need to see is the resistance dropping - that verifies the heater works, and has been consuming power.
Tip: If your meter is autoranging, lock it into the lowest ohm scale to prepare it for your quick-draw contest. Nothing like these modern meters...
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Art Benstein near Baltimore
Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you're a mile away and you have their shoes.
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Could anyone (Art, If you are there) tell me which terminal of the ECU I should ground in order to put the injection system to idle state? I’m trying to rule out the TB switch and wiring as cause for my higher idle (900, not too bad). I can not tell from my green wiring book. It’s either #2 or #3. #3 directly connects to the TB switch. #2 connects to the other terminal of TB switch, also connects to #7 of the ignition module. With the TB switch unplugged, the idle is the same. So, I’m suspecting either the TB switch itself (not likely. Since I carefully adjusted it after I cleaned the intake. I even tested the two switches for throttle plate position using multi-meter). I think that at idle my TB switch is not able to tell the ECU its position.
Here is something I did with the 20 minutes I have tonight, after the kids went to bed.
1. Pinching the hose to the IAC kills the engine immediately ---- no un-accounted air.
2. Short-circuiting either of the two wires on the TB switch plug to the middle wire did not affect the idle.
3. The FPR is old. I’ll replace it as soon as I get a chance. However, it’s not leaking fuel when I pulled the vacuum hose. When I blow into or “suck” on to vacuum hose, there is no affect on idle.
Art, there is power to the O2 sensor heater and the heater resistance reading looks fine. However, I decided to replace it with a new one (only 37 bucks from AutoZone).
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Hi Erwin,
The idle switch uses pin 2 on the ECU. Pin 3 goes low when you push the throttle wide open. If you back probe pin 2 (it is the yellow/white wire) you should see close to zero volts on it until you touch the accelerator pedal. Repeat that test several times to judge the repeatability of the microswitch contacts.
I'm unaware of any test point to ground that disables the idle valve, like the LH2.0 has (83-84). 900 rpm wouldn't bother me much, just as long as the car didn't want to leap ahead if I lifted my foot from the brake. I'm not all that certain the dash tachs are trustworthy to that degree at the low end.
When you check that voltage, be aware the ICU is using the same signal in parallel. Also a yellow white, but on pin 7.
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Art Benstein near Baltimore
Why does Sea World have a seafood restaurant?? I'm halfway through my fish burger and I realize, "Oh my God.... I could be eating a slow learner." (Lynda Montgomery)
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maybe it's the $37 o2 sensor. I read here you should get the direct fit bosch unit.I paid $129 from FCPGroton not long ago.I had code 2-1-2 before switching it out.
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