Using Intake Cleaner Question 3.2L-Rough Idle
 

I have checked all of the sensors and get the right voltage or resistance, except the O2 sensor. Can't get it under 13v, no mater where the air flow screw is adjusted? Have checked for vacuum leaks and can't find any. I did read somewhere that a hose goes to the vacuum advance to the master cylinder. Not sure where that connects. Will a dirty AFM cause an O2 sensor reading like this? Can I spray intake cleaner directly into the AFM? The can directions say not to spray directly into any mass air flow units.

Normal is 0.1 to 0.9 volts DC. If you're getting 13+ volts then sensor is bad, meter is bad, or you're not testing properly (wrong DMM scale, or O2 sensor is outside proper operating/testing temps -- 600F+ per Bentley). Or perhaps you're reading the wrong wire; if you have a 3-wire O2 sensor you could be reading the battery-side voltage of the heater lead and not the sensor output lead. I don't think even wideband O2 sensors have 13+ volt range, even if bathing in liquid fuel 13VDC is way off.

No. O2 sensor voltage drops w/lean condition (> ~14.7:1 stoichiometric / ~1.0 lambda). If running rich enough to show 1.3VDC (much less 13VDC) then it'd be so rich I doubt it would run at all. Wouldn't be vacuum leak either, as false air would cause it to run leaner -- not richer -- than AFM measures.

Am assuming, per your garage, yours is 1987 3.2 Motronic w/stock AFM. AFM uses a movable flap/vane to measure incoming air. Combined w/air temp sensor to adjust for air density, this is what measures intake air for DME computer. If you inisist on cleaning your AFM, pull it off the throttle and use short bursts of CRC Lectra-Motive (red can, available at your FLAPS) along with a toothbrush and paper towels to clean the inside of the AFM. Better access if you remove, and you'll get all of the crud that way. But, per above, it's not the cleanliness of your AFM.

Again, assuming yours is 1987 3.2 Motronic, you do not have MAF (mass air flow). MAF uses a heated, thin gauge wire (made of platinum, I think) to measure air flow. As air rushes by the heated wire, the wire cools and resistance value changes. More air flow = greater cooling = more resistance change. Each MAF has a specific output that -- based on the cross-section of the sensor (diameter of tube) -- transaltes into voume and density of air to the engine management computer. You shouldn't use any kind of chemical cleaner in a MAF since they can leave a residue on the wire which leads to out-of-range readings. Besides, MAF sensors almost always incorporate a short heat-up cycle of the wire on start-up to burn off any contaminants. In short, they're designed to be self-cleaning.

How about providing a few details of running condition, and what's happening w/your car's performance that's leading you to these diagnoses? That'd make it a little easier to help us point you in the right direction.

Dale

87 carrera is stock, except for test pipe, Wong chip and sport exhaust. Have replaced DME relay and checked every vacuum hose and replaced them if they just looked bad, except the one going to the brake booster. New plug wires and plugs. Sent the injectors and had them reworked. Sprayed the engine with brake cleaner to check for a lead, no luck there. Have a rough idle I can't smooth out. At times, seems I have more horsepower. Sometimes, from a stop, the car runs like a bat of Haites and seems to have awsome pull. next time from a stop doesn't seem to run as good, but runs smooth as it accelerates. Driving normal and shift into 2nd get small backfire thru the exhaust. If I'm cruising at any speed, I can feel a light surge of power. Does seem to run smoother at higher rpm's. After 4K rpm, seems to pull better, as long as I have her under accleration. About the volt/ohm meter. I have it set to auto and might have been 1.3v, if thats possible. Maybe, .13v

IIRC, an earlier thread of yours said you cleaned your ICV? Might want to double-check its operation - momentarily jumper 12v to terminals you should hear a click as the valve opens/closes.

Based on what you've already done and the idle/backfire symptoms you note, sounds to me like an ignition/ignition timing issue. If it were me, here's what I'd check (or replace) if you haven't already:

1) distributor cap and rotor
2) check ignition coil (I assume you replaced coil lead when ignition wires replaced)
3) pull plugs and check condition
4) run w/borrowed - and known good - DME to isolate whether that's the issue
5) check clearance of crank position and timing sensors
6) re-check output of crank position and timing sensors while moving their lead wires (can get inconsistent readings if insulation on wires is heat damaged/cracked), these can give occasionally good readings (false positive)

Try re-testing the O2 sensor, making sure your're measuring the output leads and not the heater lead. If you're still getting 0.13 volts your O2 sensor has likely gone south -- should fluctuate. After re-checking voltage and finding constant reading, unplug O2 sensor and drive the car a little. Won't hurt it; just will run in 'open loop' condition. See if some of your idle/backfire symptoms go away; will help confirm O2 sensor as a cause.

Be aware, though, you might have multiple issues contributing to this running condition.

Hope this helps, and good luck.

Dale

I checked my meter on the battery, to be sure it was working and got 12.8v. No mater what combination I put the leads on the O2 sensor, I get some crazy volt reading. I left the O2 sensor unplugged and the car idles smooth and accelerates a lot better. About 6 months ago, I replaced distributor cap, rotor, plug wires and fuel filter. Does this point to a bad sensor?

Same thing happened to me about 4 months ago. O2 sensor went south; drivability was so bad -- stalled on freeway -- I had to disconnect sensor to let it run open loop so I could get home. New O2 sensor, runs like a champ.

Dale

Thanks, ordering one now. Maybe, this will fix the idle that has been driving me crazy.

Not sure whether you resolved your problem but I have just finished going through the same pain and finally tracked most of the issues down to a faulty/dirty transmission earth strap. Went through all the same checks:replaced all general ignition components (CHT, plugs, distributor cap&rotor) plus fuel filter and pump and ultrasonic clean of injectors. It wasn't until I removed transmission earth strap and cleaned connection points that problem basically went away

I replaced O2 sensor, must have been bad, I'm getting .5 v from it now. I checked all the grounding spots and did clean the strap your talking about. My clock started working part-time, wonder if there is a bad ground somewhere that could be causing idle-performance issues? Thought about putting the stock chip back in and see if that changes anything.

Any update? Did the new O2 sensor resolve your issues?

it helped A Lot. I get .503 to .507 v from the O2. From what I have read, should I get .1 to .9 volts? By the way, I cleaned the AFM and installed the new O2...It helps to connect the hose on the air box. :D I'm playing with the mixture now and seems to ge getting better. Turn 1/2 and drive some, turn another 1/2 and so on. I have it 3 turns out. Idles a bunch better. One thing for sure, I know where all the vacuum lines go. One question: some vacuum lines are wrapped cloth and some are plain ol rubber. Is there a difference with these? Last but not least- thanks for all the great support, without you guys helping the car would never run.

My '89 never really idled at the spec'd 880 RPMs...no idea if it (base idle) was ever tweaked, as the yellow cap was in place and looking quite original...decided today to pop it off (it crumbled-basically) and have a go (with jumper in place.....). The process worked quite well,..as she dropped idle (a good bit) when the jumper was applied. THIS, as I understand it, should roughly center the ICV, essentially for a baseline point for the DME. My adjustments brought on changes, for sure. I could never really hit the exact spot I wanted with jumper in place),..but a slight tweak (jumper off) placed her at 890 RPMs,..and that's where I left it.

I, too, checked my O2 sensor's output,..and found it to be dead on 51 DC millivolts (.051 DC volts),..so I was reasonably content that all is well. I have yet to TOUCH the mixture, without getting my hands on a wideband sensor. Unfortunately, no one else at home to rev her while watching me meter......I'm gonna' get the mix checked next, as I understand these 2 adjustments are itterative (base rpm idle & CO2/HCC mixture).........as the engineering type would be: I'm not about to "tweak" anything without the instrumentation,..hello Lambda, I'd say.

I think it's time to freshen her up with a new O2 sensor (preventively)......why not?

Good work!

BEST!

Doyle