97 sonoma bucks/surges badly, tach incorrect

[bricklinwall]

I have a 97 GMC sonoma 4.3L. After driving 140 miles one day it began bucking/surging at mid throttle. When you pull a small hill you have to floorboard it and the fastest you can go is 20-25. If you hold it at half throttle it bucks so hard you'd think it would fall apart but smooths only if you floor it, but will still only go about 30mph max. Also the tach reads about 1200rpm higher than it should at all times. We've already replaced the in-dash wire loom (which had some burned wires) and everything else we can think of. Could it be the electronic advance or the fuel pump? Thanks.

[geogrubb]

I had a similar problem with an 86 astro, try replaceing the plug wires first, if that dont fix it have the fuel pump checked.

[fuglyvortec]

I've got a 98 Noma 4.3, had the same problem about three years ago. Don't worry, it's nothing major. More than likely, it's your mass airflow sensor. Once the element inside the sensor becomes dirty and can no longer self-clean, the computer no longer knows how much air is entering your engine, so it can't adjust fuel flow to match. Your check engine light should be on in this case. If that is so, have your codes pulled. You may have secondary codes thrown because of the airflow sensor not operating correctly.

If that is the problem, Granatelli offers a performance airflow sensor that is cheaper than the stock replacement, and offers a few extra horses because of the wider bore.

One other thing you may wish to replace just to be sure is your TPS (Throttle Position Sensor).