MAP sensor question

I would like to replace MAP sensor (locate on throttle body). Is there a procedure to perform this task? Can I just unplug and un-screw the 4 screws
then replace with a new one then drive? The reason I am asking about this because I am suspecting a problem (intermittent)with this device and have access with another from a diff car with the same engine to test it. Is there a risk of doing this?
Thanks in advance for all your help!
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NOSPAM wrote:

Swapping it out should work just fine. Run your car through a few driving cycles afterwards.
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If you have changed the wires, coil and spark plugs already, then perhaps you should check out the fuel filter and have the injectors cleaned. How many km are on the car? Injectors should be flushed every 100 000 - 120 000 km. You will notice a huge difference. I had the same symptoms on my Olds 3.8 FI. Flush the injectors and change the fuel filter. That'll do it.
Let us know how it goes Mark

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map sensor?? 4 screws???? just want to make sure you are changing what you think... You might have a lot more luck with the int problem if you give us year and model and engine and such....It is late, but I am thinking you are talking about a MAF sensor..... some are different.... Bobo

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Sorry! you are right! MAF sensor It is on 1992 3.8L engine

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whats the problem?? I have changed a lot more of other parts in that engine that the MAF sensor.... int stall?? SES light??? no start?? Those aren't the kinds of MAFs that used to fail just by tapping them, and they don't fail it that way,usually.as far as changing that one, there are 2 different models, if you pull it off,look for the o-ring... there can be 2 different bore sizes.You will see what I mean if they are different when/if you try and swap....

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Thanks bobo for the info. Here is an additional information in attempt to understand this problem Vehicle desc.: 1992 Pontiac Transport SE Engine: 3.8 L Odometer: ~ 156,000 km
Problems:

"D") is about to switch to final gear

gas pedal to about 1/2 inch down to increase engine rpm, the transmission would down shift and the problem would goes away. > If I drive faster such as 120 km/h, I don't notice as much or at all since the engine rpm would be about 2700 rpm as compare to 1800 rpm.

briefly (he did road test and plug in the scanner) and he said he does not believe it is however, further in depth testing will be required.

switch off the overdrive mode to drive. You can tell this by an increase in engine rpm (same engine rpm as in drive mode).
So I can safely assume that this engine hesitation problem, or engine shake just before downshift or overdrive problem all have to do with engine rpm. Perhaps engine vacuum or engine response to load needs to be verified. I have tried my best to ensure proper vaccum connection is good condition.
Below is the list of items within the last 12 months that I have recently done to the vehicle as part of regular PM 1/ Replaced spark plug AC Delco and wires (Canadian Tire) about 10 months ago 2/ Replaced one ignition coil 3/ Replaced transmission oil and filter 4/ Replaced coolant and engine thermostat 5/ Pass E-tested (April 2003) 6/ Air filter K/N (cleaned 2 months ago)
I don't have any problem with any fluid level (engine oil, transmission oil or coolant). Never had any problem with engine temperature. Engine always starts.
As you can see that I have tolorate this problem for many years and drive this van without concern that it would brake down. It is however bothering from time to time and would like to know what is wrong. I do have access to MAF sensor from my other car 1993 Bonneville SSEi that is running perfectly.
Regards, Paul

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Sounds like you have been going at it for a while... I only have 2 ideas.... did you try a cap and rotor yet??? what you are describing is either a trans prob, or a secondary ingition breakdown.... it sounds more like a trans prob than ignition, but that is a cheap thing to try... as for the trans concern you would have to get a lot more in depth to find out what's wrong.... does it do it more when it's wet out?? if it does, then I am thinking igntion. if you put the car in drive and brake stand it for 1 to 2 seconds, does it do the shake you desribe?? what about reverse?? if it does it in drive, does it do it when the shifter is in low?? don't do this continously, or for a long time, make sure to let the car idle for a bit in between tests as to let the trans cool down..

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The car does not have cap and rotor. It is ignition modules. The car drive like normal, accelerate beautifully. I can hose down the engine with water and it would still run without problem so it is not wires. What do you mean by secondary ignition break down? I will test the wires again and perhaps bringing the van to a tranmission shop for their opinion since I have not done that. I think if I can increase engine RPM by about 500 rpm, my problem be solved but then again, I would polute more!! Paul

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Secondary ignition breakdown is the coilpacks(ignition modules), and wires, my apologies on the cap and rotor, I thought they still had those on the 3.8 in 92' .as for the shake, let me know if I am describing it right or not... You are feeling a shudder as the car is shifting into 3rd gear and also the same shake as you go up a hill big enough to kinda lug the car, but not big enough to make it downshift on it's own.. If you accelerate and make it downshift, the shuddering stops.. As far as I can tell, it does sound like a trans problem.. Best of luck.... Bobo

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I have encountered a similar problem with my 95 Beretta...it would get a shake or shimmy in a high gear underload. The problem was a fuel injector nearing failure, perhaps a weak internal return spring. Does the car set a code?
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no, no engine code yet! I thought about fuel injectors but since the van is running smooth during acceleration so I rule this out. Should I have them cleaned by the garage? Is there away to tell which one is bad if the cleaning job does not help? Paul

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Hi I had the exact same probem on my 1988 Olds 98 with 3800, shuddering while in over drive, around 70-85kmph. I would just shift it down manually or step on the gas to down shift. The car was like that from the day I purchased it used, about 80,000 to about 150,000 kms at which point other probelms started to show, like rough idle and stalls when idling. I did all the usuall stuff like plugs , wires, cleaning throttle body, tranny checks, etc. I finally did a compresion test which showed that cyliders 1 and 6 were down to
about 75 lbs. Turned out that I had 2 burned exhaust valves. I had the heads rebuilt and replaced them myself. Man, what a difference that made in power and also the shuddering in overdrive is gone totally. The engine pulls really nice in low rpm under load. Bottom line is I think you have a loss in power.
Ted M
NOSPAM wrote:

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Wow, thanks for the information. I took the spark plugs out and replaced them recently (few months ago then I parked the van) At that time, I have carefully observed the spark plug condition to ensure it is burn clean (tan in color) Also, I have had the car e-tested and it passed with great margin. So I don't think the valves has anything to do with this problem because if it is, the car would not pass e-test. Someone has mentioned that could be injectors so I will have this cleaned tomorrow by GM dealer. I will monitor it within a few days to see if the problem go away. I guess I am holding off the MAF sensor for now. Regards, Paul

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Hi My plugs looked great, even on the low cylinders. I would get a compression test to rule out valve problems. My neighbour replaced 2 MAF sensonrs in the last 5 years (different vehicles, both GM). In both cases the MAF code was set, the car would idle great but would die when stepping on the gas, could not even back out of the garage. If you can drive and there is no ECM code then I think the MAF sensor is OK. Ted M
Paul wrote:

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Well I decided to have my injectors purged by GM and the problem is now solved. So it is not a transmission problem which is a good news. I thought I pass on to everyone here. Thank you all for your opinions/suggestions.
Paul

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glad you got it fixed......kinda don't understand about the injectors, but I am probably picturing it wrong.....kinda hard to diagnos everything over the net, fun to try though

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