QuestionI have a 1989 S10 Blazer with 4.3 V6 and 130,000 miles, automatic transmission. I have maintained it myself, when possible, since new. My son has been driving it, and it began stalling when no gas is applied.
When the key is initially turned on, the Check Engine light is on. The engine starts normally with higher RPM, but sounds rough. When the idle slows down, it is very rough and will die. Before it dies, the check engine light comes on/off or flashes rapidly. After dying the Check Engine light will continue to flash randomly until it is off permanently. If the key is off and turned back on, the Check Engine light may be off or on. The engine will still start, but soon dies.
I have checked ECM grounds and 12V power, and disconnected and checked all connectors. I have seen a code 3.4 (MAP sensor) and 5.1 (ECM or PROM). Normally no code is set. I feel these are not the cause of the problem because they've only been set once each.
I feel that one of the sensors may be providing higher than it's rated input to the ECM, but don't know where to start. I've looked through online resources, including yours, and haven't seen similar. I have a factory manual, and have been going through troubleshooting procedures that are not conclusive.
Thanks for any help!
AnswerHello Bob,
Sounds like a vacuum leak to me.
That could also explain the MAP code. MAP is manifold absolute pressure, which is vacuum.
The map sensor could be correct, and it could be detecting a low vacuum condition.
Possible causes are a stuck EGR valve, a leaking intake manifold or throttle body gasket, a leaking brake booster, a bad pcv valve, or a leak in accessory vacuum system like a/c controls etc.
Another remote possibility is a plugged exhaust system, like a melted down catalytic converter.
Van
