'91 900 stuttering - Air Mass Sensor?

Question

We started having trouble at low rpm about a month ago. Idle is normal. In the last week, we could barely get the car to move. Idle still normal, but like a vacuum leak kind of feeling - major hesitation when trying to rev. Our guy is always busy busy busy, but will give us some advice over the phone. He said look for cracked or disconnected hoses and wires, etc. especially around the AMM. Everything looks in order, but I unplugged and replugged all electrical connectors, and blew out the AMM just orally. It ran fine for a trip around the block. The next day my wife took out the car in heavy rain, and said she barely made it to her meeting. When she got home I repeated the process, but also sprayed some WD40 into the AMM plug, and a little into the device itself for good measure. I know this is probably inadvisable. I wanted to use tuner or carb cleaner, but the parts store was closed. Anyway, it worked. The car runs fine now, but for how long? I can't say for sure that the AMM is the problem, but it looks this way. There is plenty of spark, and fuel in the rail. Is a big dose of carb spray at all useful? Also, is there a way to diagnose the AMM at home? I noticed that the car sure won't run if the plug is disconnected!

Thanks! I wish I could search old posts, but that doesn't seem possible right now.

Adrian · Accepted Answer

robobass  gurgled happily, sounding muchlike they were saying:...which suggests that the vac and IAC are both fine....which suggests that the AMM isn't _totally_ fubar.Bosch or Lucas injection?Turbo or n/a?All the basics are clearly at least roughly right, since it runs and idles, but have you gone over the ignition and made sure it's all good? Timed right, advancing correctly, good plugs/HT leads/cap/arm?A good spray of carb cleaner around the AMM won't hurt anything - I forget how the Bosch AMM works, but the Lucas meters the air passing through a small venturi parallel to the main flow - which is worth getting to.Google seem to have orphaned the groups archive, unfortunately.

robobass · Answer

Thanks for the reply. Nonturbo, originally sold and still in Germany, so I think Bosch. The sensor is a big piece of pipe just past the filter. I haven't changed the cap/rotor since I got the car two years ago, but the wires are fairly new. I don't suspect anything in the ignition chain since the problem has so far been unaffected by dampness, and actually worsens as the car warms up. The plugs have seen better days, I must admit, but besides wear, I don't see any indicators of other problems. Could excessive gap cause problems like this?

Adrian · Answer

robobass  gurgled happily, sounding muchlike they were saying:2.0 or 2.1?Yeh, Lucas was only on turbos.It's a quick, cheap and easy diagnostic - I'd be doing plugs, cap & rotor as a matter of course. If it's a 2.1, the ignition's much more complex, AIUI.

robobass · Answer

Yeah, basic 2.0 16v. The parts stores open in the morning. No weekend hours here! I'll do the plugs/cap/rotor, as a matter of course but I really think I'm dealing with something electronic, and AMM related. I'll report back in 24! Thanks, Rob

robobass · Answer

Well, I changed out the plugs, sprayed out the cap with WD40, andsprayed a generous dose of carb cleaner into the intake through theAMM. On a short test drive it runs perfectly. We'll see...

PeterD · Answer

I'd suggest replacing the cap and rotor if that helped it. Cap/rotoris not that expensive.

'91 900 stuttering - Air Mass Sensor?

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