[rfmaster]

Originally Posted by cyberpine

The fuel pump, filter, tank and gas were all replaced. Fuel pressure is fine, but we did have rust in tank at one point. Mechanic pulled up the TBI and says injectors are shooting smooth and consistent.

This last mechanic checked that the IAC (Idle Air Control) sensor was clean and will check the gas filter again.

My check engine code has alwas read error 34. Map Sensor voltage low.

We are thinking of changing out the Throtlle body Position Sensor (TPS).

By the way, can somebody confirm exactly where the TPS and IAC value and MAP sensors are exactly on my truck on this grid?

Many Thanks!

Locate and a take a close look at your MAP sensor. It should have three wire connector (usually with a green tab) with the following three wires:
PIN C Gray +5Volt supply
PIN B Light Green MAP signal (to ECM)
PIN A Purple (or brown or sometimes tan) Sensor Ground

Disconnect connector, with ign on, engine off, measure voltage at Pin C. It should read 5 volts. If there is no +5Volts at PIN C look for harness breaks or bad connection between wire and pin inside connector.

The other common fault is open circuit at PIN B - sensor output never reaches ECM.

Changing TPS at this time is a waist of money. You can verify if TPS is functional without removing it from TB. Just disconnect harness connector and measure resistance between C & B. At idle throttle position you should see about 4.5 kOhm and at WOT should be about 0.9 kOhm (or 900 OHms) resistance should change smoothly as you move throttle shaft between the two extremes, Final check is measure between PIN A & C - you should measure about 4 kOhm.

To do these simple checks requires DVM - any parts store should have one for less than $20. Learn how to troubleshoot and post your findings.

//RF