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warm start very rough!


New Member
April 19, 2011
Reaction score
City, State
Holt, Mi
Year, Model & Trim Level
94 Ranger STX
Hey everyone! I have a 94 stx 4.0l and have been having some issues. First off it smells like it is running very rich and im am getting horrible gas mileage (not sure the actual mpg).
Second, truck starts fine when cold but after it warms up and I shut it off and then go to restart after about 10min it is very rough and almost stalls. I have seen posts on here about this problem but nobody has said if they fixed it. After you give it some gas then it drives ok, still feels like I have a miss and runs pretty doggy.
I have done some trouble shooting and this is what I got: checked fuel pressure (30-32psi), pulled vac line from FPR and no gas leaking. I know that doesnt mean that its not bad. I pulled the plug on the MAF and drove for a little while, it seemed to run a tad bit better but still had the warm start issue. I just went out and pulled the codes. KOEO-111 CM-157/158 KOER-111. Now I assume that the 157/158 codes are because I pulled the plug on the MAF but I'll let you guys chime in.
Also, if I restart the engine (when hot) right after or within a couple min it starts fine. Its only after it sits for about 10-15min give or take that it starts to fumble. I drive all day everyday and this drives me nuts. I will clear the codes and pull the codes again tomorrow to see if the MAF codes come back.

Thanks guys!


June 14, 2012
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City, State
BC, Canada
Year, Model & Trim Level
'94 Explorer Sport mt
I hate resurrecting a 2 year old thread, but it's better than writing a dupe post about the SAME SYMPTOMS.

I've experienced this a few times myself. It seems to have gotten more frequent with cold weather setting in.

Anyone know what is causing this? Starts and runs fine when cold, starts SUPER ROUGH occasionally when warm. I have new plugs and wires, haven't had any other issues, runs pretty solid otherwise. 260,000 KM, '94.

Are vacuum lines the first thing to check? Or should I start with pulling the codes and test-driving with MAF disconnected?

My temp sensor tends to float around a bit. That's after replacing a couple of thermostats to get a "stock" one that works properly and doing a coolant flush. No other anomalies to report otherwise.


Used to be a road here.
Elite Explorer
November 21, 2013
Reaction score
City, State
Phoenix, AZ.
Year, Model & Trim Level
1994 Explorer Limited
It is a bad Temp sensor.


Been here, done that already on the 94.

There are (2) sensors, so make sure you change the one that has a cone on the end of it, next to the thermostat housing.