Hi,

As a followup to the post " '89 SE nightmare: intermediate stalling at any given time": what my car (222k miles) had been seeing was some intermediate stalling problem where the car would stall for no apparent reason while it is cruising, or when idling, or when slowing down. It could happen on any given day at any given time: for example, the car ran fine for about 2-3 days, then started stalling again. This started happening after giving the car a tuneup with a brand new cap, rotor, set of wires, and spark plugs. In many of those cases, I was getting a code "12", which indicated a malfunctioning MAF sensor. I had received several feedbacks regarding that post, and this is what I have done since;

* Replaced MAF sensor on car with remanufactured sensor of same 5-pin configuration. (For some reason, there are two variants of the MAF sensor in '89 ... one is a 4-pin configuration, one is a 5-pin configuration, price difference is 3x's more expensive on the 5-pin configuration) I thought that was the most logical step to take since the computer's telling me that this sensor is bad. Well, the car ran and stalled even more frequently with the store-bought MAF sensor than the original sensor! Returned this sensor back for a refund.

* Checked, cleaned, and adjusted the contacts on the MAF sensor connector on wire harness to MAF sensor. Made no difference in stall frequency.

* Wiggled and squeezed wire harness leading from MAF sensor to firewall on the car. Car did not stall, which seemed to indicate to me that wire harness on car may be okay.

* Replaced car battery and "hard reset" ECM by disconnecting battery for 24 hours before plugging the battery back in. No difference.

* Replaced fuel filter on car; old one had 50k miles on it. Car ran okay for about a week, but stalling problem returned.

* Replaced ignition coil because old one slightly out of spec. Replaced at same time as fuel filter. No difference.

* Replaced OEM oxygen sensor (with 220k miles on it) with new Bosch sensor. Somehow, new sensor causes "Check Engine" light to come on when car was restarted when engine was fully warmed up. (Ex: driving to store, stopping there and picking up some stuff, return to car, start engine, drive off for about 5 miles, then "Check Engine" light comes off) "Check engine" light in this case associated with oxygen sensor. Old OEM sensor was plugged back in, and light never came on. Returned Bosch oxygen sensor for refund. During this period of the Bosch sensor being on the car with the "Check Engine" light, supposedly stalling wasn't as frequent, but still there occasionally.

* TPS connector: I disconnected the connector from the wire harness, and saw some green corrosion on the TPS's contact. I cleaned it with electrical cleaner until it was nice and shiny again. Reconnected everything, but still had same intermediate stalling problem. Had hard time trying to check the specs out on the TPS with an ohmmeter, based on how Haynes expects you to test it. With the throttle closed (no gas pedal), the contact between pin A and D (or A and C .... I can't remember off the top of my head) was continuity, and with throttle partially or fully opened (some gas pedal depressed), the continuity is gone, which is what is expected. There was some other reading that Haynes suggested could be pulled from the TPS, but I was unable to find the right pins to get that reading.

So this is where I stand: car still has the same intermediate stalling problem which got worse yesterday night. According to my sister who drives the car, she says the stalling usually occurred when the car was slowing down or when it was at a stoplight. And I pulled the codes from the computer, and once again, got code "12": bad MAF sensor, as being the culprit.

I did find something really strange: if I took a screwdriver and lightly tapped the "circuit box" portion of the MAF sensor, the car would stall. However, this was not repeatable, as in some cases, when I would still tap the "circuit box" portion of the MAF sensor, the car engine would still continue to run. I still am not very convinced that the MAF sensor is fully functioning, but all the readings coming off the MAF sensor seemed to indicate otherwise, and the fact that my car for some reason ran *worse* with the remanufactured MAF sensor over the OEM sensor in the car seemed to say otherwise. The connector, I took a small screwdriver to bend the contacts inside the connector downward with the hope that maybe there was just some bad contact between the connector plug and the MAF sensor, but alas, no difference was noted.

Therefore, asides from trying another oxygen sensor (another Bosch; I told the parts counter guy to just get me another one, even though he wasn't very convinced that a oxygen sensor could be bad out of the box, simply because of the fact that my light comes on with their oxygen sensor but not with my OEM sensor), can anyone else suggest any other possible culprit behind my problems here based on your own experience or from what you've heard? I'm still *very* hesistant on buying another 5-pin MAF sensor, given that the remanufactured cost was in excess of $500+, so a used MAF sensor may have to be in the works...

Thank you for any help you can provide me with,

-Alan Quan

P.S. >> As a maintenance tip: make sure that when you replace the upper and lower radiator hose, replace the small hose that leads from the radiator to the intake manifold bleed bolt as well. Mine sprung a leak two nights ago because the rigidity of the small hose on the inside was not there anymore.

 

Ok here's to convincing you (and the rest of you out there) that the problem lies with your MAFS. Recently I told you that I lucked out and got a used MAFS for $80 bucks from my friend who works at a body shop right? Well, upon installing it on my max and running better than ever, I decided to crack open the rectangular pin connetor box of the old one... Basically I unscrewed it to see what's the inner workings of this thing. After doing so, I found out that the process is IRREVERSIBLE! But I did see what was causing the problem. Three of the pins were just burnt... Well darker than the other two. This told me that current was not flowing as efficient as it was meant to be. The fact is that the sutter connecting the pins to the circuit box on top THE MAFS was burnt and corroded. About the five pin thing, well, actually four are actually connected - one is a ground. Just get another MAFS. Avoid the headache.

 

True, but my question is then this: why would a remanufactured MAF sensor cause the car to run even worse? The stalling frequency went up considerably with the new MAF sensor over the old MAF sensor.

Oh, I did buy the 4-pin sensor first because the price on it was $180 versus the $520 for the 4-pin sensor. My car just would not run at all with the 4-pin sensor.

(And yes, I'm tempted to break open that rectangular connector box, but since you mention the proces is irreversible ..... maybe I should get a used MAF sensor first ...)

 

A rebuilt MAFS shouldn't cost you more than $250. Also, if the existing connector is asking for a 5 pin MAFS, then give it a 5 pin MAFS. Nothing more, nothing less.

 

Well, the 4-pin MAF sensor was about $170 at both Kragen and Autozone. The 5-pin MAF sensor, however, leaped up to anywhere from $420 to $470. My car is the 5-pin, and I only found out about it after I bought a 4-pin MAF sensor and took off the connector on my existing MAF sensor, only to discover that my car had the 5-pin connection ...

A local junkyard has a used MAF sensor with 5 pins for about $75. I may just choose that route. But first thing first, I'm going to install another Bosch O2 sensor this weekend to see whether it improves the driveability of the car. Granted, the Bosch sensor has 4 wires coming off of its sensor whereas the OEM one has three (with one that acts as some type of grounding shield around another wire, which makes four at the plug end), but I can't imagine this one single wire difference would cause the "Check Engine" light to go off on my car with the first Bosch sensor I had.