I have a 1986 Pontiac Fiero with the 3800 motor. The car stalls when coming to a complete stop quickly. It surges and idles high for like 5 minutes after you start it then it goes back down. Sometimes the car cranks but wont start unless you unplug the map sensor. After it starts I usually just plug it back in. I feel like I'm getting like 15 mpg and I'm not really sure what to do. The two engine codes are 1 to many volts to the map sensor, and 2 low volts to the map sensor. I have replaced the map sensor and throttle position sensor and it seems to make it worse. I'm not really sure what to do now. Any advice would help. I live in Portland Oregon if someone knows someone near that might be able to help. Thanks

Zach: The problem that you describe can be any one of a number of things especially a defective sensor, ignition or fueling problem. You can start by going to a chain auto store as many of them will come out and use a code reader on your OBD port to determine if there are any DTC's (trouble codes) . While the codes do not always indicate a specific problem they can guide you to the problem. If you can invest in a PCM scanner, laptop software or find someone locally that can help, that is a better way to focus on the problem. On modern computer controlled engines that is the diagnostic route to take.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

Manual or auto?
S/C or N/A?
OBD I or OBD II?
What mods to engine?
Is this a problem that just cropped up or has it done it since the swap?
If it just cropped up, had you done any work on it shortly before the problem started?

[This message has been edited by olejoedad (edited 03-17-2021).]

Manual, supercharged, has always had the problem since I got it.

Get the scan tool on it and start checking for vacuum leaks.
Base of the supercharger, vacuum hoses, throttle body gasket, vacuum routing, etc.