98 lt blazer with about 148000miles on it. idles very rough and stays close to 500rpm at idle and the oil pressure gauge is around 20 until you hit the gas then it goes up to 40. had the distrubutor replaced about 4 months ago. spark plugs are fine. got new tires and there is a squeak coming from the drivesahft which needs to be re greased. stock tires were a 235 70r15 and new ones are 235 75r15. could that cause any problems??? any help is greatly appreciated. thanks
-joe

 

I would go through the typical cleaning tasks of MAF, EGR, and throttle body. I bet your idle quality is affected by one or more of those things being dirty.

Larger tires would not affect engine operation. It would affect your shift points in your trans though. Not in a negative/harmful way though.

 

i will try cleaning those but the issue is the oil pressure goes down off gas and up on gas. and the same thing happened to my grandpa on his jimmy. the oil pump went and now he has to put a new engine into it.

 

Oil pressure is a function of engine RPM. If it were dropping below 10psi, then you may have a valid concern, but 20psi is nothing to be worried about.

 

ok. so i replaced the fuse for the gauges and it was back to normal and its still dropping to 20 but no lower. the transmission shifted hard added fluid and it was fine. got a code for the maf vaf sensor and cleared it still idles rough. what next??

 

Your oil pressure is fine. Nothing to worry about.

Clearing a code really does nothing. You have to address the cause of the code. Have you cleaned the TB, MAF, and EGR valve as suggested earlier?

 

No not doing that is a weather permitting thing. too much rain. Um also i added valvoline water remover to the gas and the idling and take off is much smoother. How exactly do you clean the maf??

 

MAF Sensor Cleaning

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Thank you very much. Im only 16 and any help is much appreciated. Thanks again.