95 grand am surging

I have a 95 grand am gt with the 3100 v6. about 104,00 miles The surging first started at around 50 to 60 mph. This surging feels like a stop and go, lurching type feeling. I suspected the fuel pump so I checked the pressure but it checked out. I changed the fuel filter. I had relatively new wires so I changed all three coil packs and at first, there was a change. But the problem came back. I thought it was the spark plug wires so I changed those. That didnt help. Then I changed the plugs and that didnt help. I replaced the IAC motor and the TPS And the MAP sensor with used units but the very same problem persists. I recently did a head gasket job so I took off the plenum thinking the fuel injector o-rings had failed. While I was there I checked all of the injector's resistance value and they all had about .012 at 2kOHMS. I did notice that there was oil throughout the plenum. I dont think there should be oil there so anyone know why there might be oil? The PCV valve rattles but im thinking its letting it suck in oil. Is this a possibilty? There's no check engine light on and Im beginning to think that the computer is at fault. Anyone ever experience the same thing? The problem has gotten worse. I checked the vacuum and it is mostly steady at 19 to 20 staying at or around there. My friend says that I might have blow by on the rings of the pistons but I dont get any black or blue smoke coming out the exhaust pipes. Any suggestions or ideas from anyone would be greatly appreciated. Thanks.

I was doing some research yesterday and discovered that even though the fuel pump passed the pressure reading test, it might still not produce enough volume that the engine needs. Does anyone know how to run a wave scope test on the fuel pump and how much does the tool cost?

Have you checked for a vacuum leak?

I was doing some research yesterday and discovered that even though the fuel pump passed the pressure reading test, it might still not produce enough volume that the engine needs. Does anyone know how to run a wave scope test on the fuel pump and how much does the tool cost?


scopes are expensive $2500-8000

yes I checked for vacuum leaks and I even tightened down the intake manifold a bit more just in case. Wow scopes are too expensive. Im going to change the fuel pump this weekend.

Could it also be a transmission problem?

it cant be the transmission because now when the car starts up in the cold, the idle that used to go about 1700 rpms, struggles to get there and it surges during the process. When i get motivated (its cold out there) im changing the fuel pump and pressure regulator.

Do the regulator first is will not take that long to remove and install the new one. BTW the snow will be heading your way again. In Chicago area weather is calling for 12'' of snow and possibly more.

In your case If you already have fuel pressure gauge, see if you can get an extension so you can connect it to the injector rail close the hood and tape the fuel pressure gauge on the windshield facing inside of the car so you can see what happens with the fuel pressure when you drive on the highway at 60mph maybe this can tell you something about the fuel pump if you see needle jumping and you know that your fpr is good.

well I changed the fuel pump and the pressure regulator...not a hard job at all...but the same problem exists with the rough idle, a little stumble at the beginning of acceleration and a surging anywhere over 45 mph...the only things left are the EGR valve, catalytic converter or quite possibly the intake manifold gasket...when i asked my friend what 120 inch pounds was he wasnt sure and suggested that I torque it to 15 foot pounds. That was when I did the head gasket job and this current problem occured about a month later..I later found out that it should have been only 10 foot pounds so Im thinking i might have cracked it possibly. Although I get a really good vacuum...somewhere between 19 and 20 psi. That also might explain why there is oil in the upper plenum...any ideas?

well I changed the fuel pump...not a hard job at all...but the same problem exists with the rough idle, a little stumble at the beginning of acceleration and a surging anywhere over 45 mph...the only things left are the EGR valve, catalytic converter or quite possibly the intake manifold gasket...when i asked my friend what 120 inch pounds was he wasnt sure and suggested that I torque it to 15 foot pounds. That was when I did the head gasket job and this current problem occured about a month later..I later found out that it should have been only 10 foot pounds so Im thinking i might have cracked it possibly. Although I get a really good vacuum...somewhere between 19 and 20 psi. That also might explain why there is oil in the upper plenum...any ideas?
I was told to look out for the ( freeze plug under the intake ) where originaly was a distributer but was later removed and a sorta freeze plug placed in its place sometimes these leak oil or spray upwards either burning off or being absorbed into the hood mat

ok I'll look into it...I tore the engine down to get at the manifold yesterday but I didnt see any problem with the gasket...I was told that the Intake Air Temperature sensor can give the same exact symptom with a rough idle and surging at higher speeds so Im going to replace it with the older one I held onto...I had bought it new shortly be4 the problem arose. I'll keep you updated with this frustrating problem.

do not waste your money on new IAT, IAT is the last sensor that can give you any problems
MAF can have similar problems try disconnecting maf sensror then pcm will compensate using default parameter tables and you should notice short throttle choke every time you press the gas pedal but then you can drive normaly so if that constant surging stops you can blame MAF then. But before that buy maf cleaner and clean the sensor

On this Pontiac model they didnt use the MAF sensor....I'm wondering if I can clean the Air temp sensor instead..

Has anyone ever had problems with the throttle body and what kinds of symptoms did u have?

Surging of any kind is usualy only a few things;
-vacum leaks in the air intake
-fuel pump not working properly
-IAC control system is faulty
-Or emission/engine control system is faulty

-I checked all the vacuum lines and i took off the intake manifold to look for a cracked gasket.
-I replaced the fuel pump
-I replaced the IAC motor with a different one to find the same symptom
Im starting to think that the EGR is at fault or the throttle body housing is plugged up with carbon or dirt. I'll get back to you guys.

I replaced the throttle body with a different one which I thoroughly cleaned out. I also replaced the EGR valve and I still have the same problem. I guess im over my head with this problem. Time to take it to a mechanic. Keep you posted.