95 Tsp stalling

I just got a 95 Transporter - When I put it in drive, the rpm drops to about 300 then goes back to idle, sometimes it stalls. At low drive speeds (below 40 Km/hr) when I try to accelerate ( or at a stop light and try to move) the engine starts to miss - ( it does not backfire). It misses a few times then runs OK. I only have this problem moving from a stop or at low speeds; at highway speeds everything is fine. Any help would be appreciated.

First check the exhaust recirculation valve (EGR). One idea is to disconnect the plug that feeds it to see if it makes a difference..however if it is stuck in partly open position, it might not make a difference.

Thanks. I switched the ERG valve with one from an engine my friend has in his garage - but it made no difference. The van has a new fuel pump; I also changed the throttle body with one from my friend; new plugs; switched IAC valve; switched MAF sensor (on the front of the engine). The CEL is not on or flashing - so I cannot get a code. Any additional help would be a bonus.

ANy difference between starting from cold or when hot? I can provoke this problem on mine because I have tricked the coolant temperature sensor with a switcheable control and falsely sending high temp reading to computer when in fact the engine is cold does mimick your problem. But when the engine is actually warmed up, I cannot reproduce the condition...so just for a try, I'd suggest you DISCONNECT the temperature sender: this is equivalent to a low temp reading and will command for a richer fuel mixture...just see what it does. In addition to the AIR temperature sender, here are 2 ENGINE temperature senders: one for the gauge (1 wire) and 1 for the computer (2 wires): I 'll check for its exact location and come back with that info.

When I first start up in the morning or when the engine is cold, the problem is really bad - almost impossible to drive, but when the engine has warmed up (coolant temp is at normal operating temp), the miss is still noticeable, but not as bad. Should I disconnect the sensor on the air intake???
Thanks.

THe coolant temperature sensor acts on mixture, but the air intake temp sensor impacts mostly on timing, not on mixture so I would not think it could be involved in your symptoms but giving it a try is no risk.
here are resistance readings for temperature sensors (air and coolant)
www.avigex.ca/xport/thermistor.jpg

I took the van to a mechanic, and after 2 days, he says: when the accelerator is pressed - somewhere from initial press to about a quarter way down, the MAF reading goes to zero. He tried a new MAF and ECM but it made no difference. This problem ONLY happens with the transmission engaged (in drive but I am not sure about reverse), there is no problem revving the engine in park. Is there a transmission sensor or connection that sends a signal directly to the MAF?? or indirectly through the ECM??
or if there is a short circuit happening, where would I begin to look???
The mechanic says the engine runs with the MAF disconnected - I am not sure if it just runs at idles or if it actually drives - can I drive it home from the mechanic with the MAF disconnected (20Km)???
Thanks.

I'm not too sure what your mechanic means about the MAF reading going to zero..the MAF signal is kind of pulsed and is not directly readable with a voltmeter...
www.avigex.ca/xport/maftest1.jpg
www.avigex.ca/xport/maftest2.jpg
so unless he is equipped with a digital scanning system, I'm a little bit skeptical...if I count well, you have tried 3 MAF's......so I'd look for something else...although the symptoms DO ressemble the MAF issue, may be plugs, connectors.... and no, the transmission does not send codes to the MAF. confirm when you have changed the whole throttle body, you have had the TPS (throttle position sensor) changed too?..but this would not match the severe RPM dip you describe when going into "drive"... What you experience is a little puzzling....

DId someone check the fuel pressure at the fuel rail? Fuel supply is most of the time a suspect when it is not the culprit, but it may happen.....should be over 40 psi.
ANd BTW, did some one check for error codes? you said the CEL is not ON, but does it light up at the startup check?...and some codes do NOT light up the CEL..'95 is OBD2 and the diagnostic codes are quite elaborate. www.avigex.ca/xport/allpontiaccodes.txt

EDit: P.S.: As Timguili mentions in next post, this one may still be OBD1 but cannot be read from the CEL with the jumper in the diagnostic plug. THese codes from the '93 OBD1 : www.avigex.ca/xport/3800codes.jpg

I have a 95, and i am Obd1 Not 2. Half way through the model year I heard the switched over.

Got the van from the mechanic today. Drove it with the MAF sensor disconnected: the rpm fluctuates at idle ( both in park and drive); sometimes it stalls; and from a complete stop there is still hesitation when I gave it gas, but once the vehicle is moving - there are no more misses or hesitation, regardless of what speed I am driving at.
It is certainly driving better with the MAF disconnected.
I noticed my oil pressure is very low at idle - almost to the red line. At driving speeds it stays locked at 275 Kpa. Could oil pressure be factor??
Again the mechanic says the MAF reading goes to zero when the engine hesitates - resulting in a cut off of the fuel flow. However, the MAF signal is not missing for 4 or more continuous seconds to set a code - just briefly ( 1 sec or a fraction).
Once the old codes (from disconnecting sensors) were cleared, and the vehicle driven, no new codes appeared; fuel pressure is OK; new plugs;
I have noooo idea where to go from here........

I changed the spark plug wires, and BINGO!! the problems "ALMOST" disappeared. I only noticed a very very slight hesitation a few times. That was 2 weeks ago, but now the problem is back. Weird.

I had bad stalling problems with my -94 3,8. Changed spark plugs+wires, helped for a while. After that I checked all vacuum hoses, found one broken, replaced it but it didn't help. Finally I blocked the EGR valve with a piece of sheet metal: no more stalling or shaking. This i did two months ago and the engine has run perfectly after that.

Antti

I'm not too sure what your mechanic means about the MAF reading going to zero..the MAF signal is kind of pulsed and is not directly readable with a voltmeter...
www.avigex.ca/xport/maftest1.jpg
www.avigex.ca/xport/maftest2.jpg
so unless he is equipped with a digital scanning system, I'm a little bit skeptical...if I count well, you have tried 3 MAF's......so I'd look for something else...although the symptoms DO ressemble the MAF issue, may be plugs, connectors.... and no, the transmission does not send codes to the MAF. confirm when you have changed the whole throttle body, you have had the TPS (throttle position sensor) changed too?..but this would not match the severe RPM dip you describe when going into "drive"... What you experience is a little puzzling....

DId someone check the fuel pressure at the fuel rail? Fuel supply is most of the time a suspect when it is not the culprit, but it may happen.....should be over 40 psi.
ANd BTW, did some one check for error codes? you said the CEL is not ON, but does it light up at the startup check?...and some codes do NOT light up the CEL..'95 is OBD2 and the diagnostic codes are quite elaborate. www.avigex.ca/xport/allpontiaccodes.txt

EDit: P.S.: As Timguili mentions in next post, this one may still be OBD1 but cannot be read from the CEL with the jumper in the diagnostic plug. THese codes from the '93 OBD1 : www.avigex.ca/xport/3800codes.jpg
Could it not be the same problem i had?
When i hooked my laptop to the car, the MAF (right upper corner) reading went to zero to and then he staled.
I had a almost broken wire the yellow one.
Maybe he has to. That explains why a new MAF dont make any differnts.

Did you just run a new wire from the MAF through the firewall to the ECM?? I would like to give it a try so any insight into how you did it would be a great help.

Did you just run a new wire from the MAF through the firewall to the ECM?? I would like to give it a try so any insight into how you did it would be a great help.
No, my wire broke close to the connector.
I have to repare it yet. But for now i have taped it.
I have to look for a new connector and put all three wires into the new connector.
I dont know where the ather end goes to, but its a good iedea to test with trhee new wires.

The vehicle idles fine in park, so I guess my idle air control circuit is OK. Anyone knows what the shift solenoid B does?? Can this be related??? When I shift into gear, which circuit takes over from the idle air control circuit??

Shift solenoids are in the transmission and alter oil passages to modulate shift points.
At neutral, park, rev and 1st: both are ENERGIZED
2n gear: A off, B on
3rd gear: A off B off
4th gear:A on B off
IAC is controlled at all times by the Powertrain COntrol MOdule. www.avigex.ca/xport/fuelinjection.jpg

So far, since changing plug wires, the rpm drop going into drive has mostly disappeared. I find if I do NOT warm the engine up properly, the engine hiccups (hesitation) are almost guaranteed to occur. However, if the engine is warmed up until the rpm drops to normal idle speed, the hiccups are not as noticeable - still there, but very intermittent. Sometimes when it happens, I can smell gas.
LMP, I noticed in another post you said you wired a resistor to your temp sensor to lean the mixture - I would like to try that - I think the engine is flooding. Please, could you give me the details?? email: [email protected]
Thanks .....

ps to above: Also, if there is a method to test the coolant temp circuit I would appreciate getting it from you. With only ONE wire, I cannot figure it out, nor how to wire the resistor in parallel.

Thanks again.

I drove the van with the MAF disconnected. I had to keep my foot on the gas because it won't idle, it stalls. But once I start moving, everything is fine - the engine does not stutter or miss. Since the MAF has been changed, should I take it that the problem lies in the MAF electrical circuit??

The 2.2k resistor I added is shown in this diagram:
www.avigex.ca/xport/enginesensors.jpg
I ran the wires inside to a switch I installed under the dash.

It has influence on the fuel mixture only when engine is very cold: tells the computer coolant temperature is around 80°F. As soon as engine gets warmer, the sensor totally overwhelms the added resistor as the thermistor gets under 200 ohms. At very low temps, sensor value is around 10000 ohms, thus the 2200 ohms resistor is dominant over the thermistor.

The leaning effect is such that at very low temperatures, if the resistor is switched in, the engine would simply not start. That is why I start the engine with resistor out, and after 30 sec or so, I can switch the resistor in. IN summer, it has no effect.

DO not forget: there are 2 temperature sensors: one (with one wire only, ground is through sensor body) is for instrument, the other (2 wires) is for the computer...

Thanks LMP

The van finally set a code: po101. From what I have found, it means MAF sensor performance. Can anyone with a service manual help me troubleshoot this ???
Thanks.

I changed a leaking exhaust manifold, and so far for over three months the problems are gone. Thanks to everyone who helped.