1990 GMC Sierra K1500 4x4
Started yesterday. It wont start unless you hold the pedal to the floor. It then spits and splutters and rocks for a few seconds until it stabilizes to a regular idol. At times it goes into a high idol. If you hold the brake, and put it in drive or reverse it dies instantly. If you let it idol for a while it runs good, but then if you barely press the gas, again it will die instantly, then not restart. We changed the fuel filter. The wires, distributor, and plugs are good. This just started happening instantly, and didn't act up over time. It has 181,000 miles and just now has had this issue. Regular maintenance has always been done. PLEASE help. Some said it may be the fuel pump, but I don't know.
Check for vacuum leaks, the line going to your map sensor. Check your codes too. Google "how to check gm obd1 codes"