johngammel

My 1988 has about 62K miles on it and is basically original. Using WinAldl with the ECM type set to 1227747 for my L98 all of a sudden at idle I have varying engine speeds. At the last car show I had to two-foot it because the idle would go 7 - 5 - 4 -3 - not running but would start right back up. With a quick check today I saw the following O2 sensor readings (and many others) all within about 2 minutes while idling:
RAW Converted (Volts)
21 0.093
102 0.451
184 0.818

The first time I started it popped the service engine light and had a 33 MAF high but that cleared out. Is it time for a new O2 sensor? Or?

65Z01

After warmup the O2 sensor reading is supposed to flip/flop between hi/lo values at steady conditions.

I would look elsewhere for your idle issues: fuel, vac, air, etc.

C409

….. Check the IAC counts … inop or sluggish IAC can contribute to slow idle and High MAF … also check for fuel in the vacuum hose for the fuel pressure regulator … a leaking diaphragm will cause a rich condition on the right bank (O2S is on the left) which will also contribute to low idle speeds … refer to the factory service manual for diagnostic flow charts to run further tests … garage queens suffer issues that don't usually appear in daily drivers … get to the next car show early and spend the extra time polishing something …..

Kevova

O2 voltage should cycle across .450 rapidly, data stream would call it "Cross Counts" . The voltage should range from .0xx to .9xx. Because of mpg standards car is designed been driven just of idle unfortunately that allows O2 to "coke up". Periodically driving at 2500 rpm clears carbon build up on valves and O2 sensor. If after driving at higher RPM sensor voltage does start to swing correctly I would replace sensor.

johngammel

Well - I do spend more time driving my '61 now that it's in really running condition than my '88. I did drive up to St. Pete for the show - nice drive up - horrible drive back in monsoon rain conditions. Thanks everyone for the suggestions - will look at other things. I do have a set of factory manuals (actually 2) for reference so I'll start tomorrow on the extended check.

aklim

Fuel pressure at KOEO and WOT. How is the spark color? How is the wire set to the plugs? Are they leaking? Check IAC counts to see if it is about 20-30

johngammel

After getting a cortisone injection in my arm last Friday I can start working on light duty again. Thought I'd start at the very front so here's what I see:

aklim

What is the question

johngammel

Does it look OK?

There isn't any fuel in the vacuum line for the pressure regulator. The IAC counts are 40-48 with 41 and 42 the predominant values.

johngammel

I forgot to mention that it's a California car. Also, the air filter is incredibly clean.

aklim

If you can see something it is FUBAR. Looks do not mean anything. It can look good but isn't measuring right. Steady IAC is good. If you had it running with everything but the motor OFF, the counts are OK. Have you tried cleaning the IAC? I would take it off and spray it gently with brake cleaner and wipe the pintle gently Take the TB off, take the top plate off and the IAC housing and clean up everything and reinstall with fresh gaskets.

How is the fun pressure? Get the pressure when you turn the key to run and see how long it takes to lose pressure after the key is turned off. After that see how good the wires are by spraying a fine mist of water AROUND the wires

johngammel

The engine started right up and ran very smoothly. Then it just quit. Below is the pic from WinAldl. Obviously the RPM drops to 0. The O2 value decreases, the MWAF1 decreases, the MCUIO increases, the OLDPA3 goes to zero after a missing data point, the BLM has a missing data point, and the O2 has a missing data point. Thoughts on my next step?

Kevova

Engine quit? Stalled? Data is after or or during?

johngammel

Just quit while idling in the garage. The first time I didn't have my cell camera ready but I did the second time. It's fine at -9 but at -7 it's quit.

Talking to one of the other guys in my club and he suggested I try MAF cleaner. He knows one person that used it and it solved their problem. I'm going to get some later today and try it unless someone says absolutely not to use it.

Kevova

TPS and IAC are incorect for idle. O2 has no cross counts and indicate rich condition, possibly degraded O2 it won't always set a code. I would check ECM grounds. There are spray MAF cleaners available at parts stores.

aklim

Can you disconnect the MAF and see if it works

johngammel

Well. I got the cleaner, went to disconnect the MAF harness and found that sometime prior to about 18 years ago someone had "repaired" all of the wires at the connector - see picture. Huh... Unless there's something I don't know I think it would be a good idea to remove the crimp connectors and use shrink tubing and solder - but it's going to be tight with the way it's cut. Would you buy a new connector with wires and solder that in? Thoughts?

aklim

I'd get a new plug and put it on but disconnect the sensor and see if the problem goes away

aklim

https://www.autozone.com/electrical-...tor/887036_0_0

Before I even go there, I'm disconnecting the thing to see if it cures the problem. If it does, I will cut the old plug off and verify the wires so I know it will be hooked up to the right wire. No telling how he did it or if it was even somewhat close, much less right. If removing the sensor does not cure the problem, I will want to investigate further before doing anything else. I don't need to add another variable to the equation

johngammel

Thanks. I'll try running the car with the MAF disconnected and see what happens.

Crimp connectors were the root cause of many of the problems that my '61 - after I replaced all of the wiring everything was fine.