Have a 1994 Mazda B-3000 truck w/ 3.0L V-6, 5-speed, EEC-IV. Truck starts right off when cold but wants to idle smoothly at 1500 - 1800 rpm even after it warms up. Initial push/snap of throttle to take off (or just to rev engine in neutral) results in a near-stall of engine and I have to let up on gas and try again to get enough revs to take off. Throttle response and acceleration during high-speed operation on road is fine. If I park and shut engine off, it will turn over fine but not start (not even a lick) until it gets completely cold. Have checked vacuum lines, PCV, throttle linkage, and air filter/intake -- all looks fine. Have unhooked IAC solenoid during the fast warm idle and engine slowed down to about 800 - 900 rpm and continued to run smoothly -- but near-stall throttle response remained. Any suggestions?

 

Welcome to FTE!!!

I would start by pulling the codes and looking for vacuum leaks.

 

Thanks for your quick reply! Double checked every vacuum line and fitting I could find and they all look okay. I did a KOEO test with the check engine light and got a single on-demand code of 116 followed by a code of 111 for the continuous memory codes. The 116 (according to haynes) is a "coolant temperature sensor out of self test range" and the 111 is a "pass".

When I start the engine cold, it cranks right up and has no lag/stall when I snap the throttle -- and it runs evenly and powerfully. As it warms up (and I verify with the temp gauge and hot radiator hoses) it exhibits the lag/stall when I snap the throttle and will not restart when I shut the engine down. The engine will restart when it has cooled completely off.

As haynes suggests, I'll pull the connector to the sensor and check the connector/wires. If that doesn't work, then they suggest replacing the sensor. Am I on the right track? Will a faulty coolant temp sensor cause these symptoms?

Thanks again...

 

The code 116 was the trick. Got a new coolant temp. sensor for $15 and put it in while i had the negative battery terminal disconnected. Waited a while, reattached the battery, cranked up and the engine runs like a top, low to high rpm, with no stall/lag when i snap the throttle. Engine starts immediately and runs smoothly, cold or hot. Not bad for 141,000 miles. Thanks again...

 

Good to hear you knocked off the problem.

Just goes to show how important each and every sensor is to the proper operation of an engine with electronic engine control (EEC).

P.S. Welcome to the FTE Ranger board!