I unplug my coolant temp sensor and my car runs better than with it unplugged, why?

40

Asked by Jul 05, 2013 at 10:25 PM about the 1993 GMC Vandura G25

Question type: Maintenance & Repair

I've replaced the coolant temp sensor, thermostat, fuel filter, vacuum hoses, checked the fuel pump, replaced the map sensor, idle air control valve, o2 sensor, cleaned the tbi and my car still has a rough idle, dies often times when you first put it into gear, hesitates and jerks when you give it throttle off of stops, has trouble maintaining cruise and sometimes dies at idle. Any ideas as to why my car will run with no problems with the coolant temp sensor unplugged but the symptoms continue when the sensor is plugged back in.  It also often times comes up with a PO44 Error code when running bad which is a lean fuel error code.

10 Answers

100

Again, vacuum leak. Check ALL hoses and fittings. The reason it runs better unplugged is because the computer throws into a richer mixture. The coolant sensor acts as a choke (in a sense). When cold, it says Throw more fuel. When it's warm, it says Okay,lean me out. There is a connection on the brake booster that could be cracked. What type vehicle is this?

3 of 3 people found this helpful.
40

I've replaced two vacuum hoses that were leaking and have looked all over the vehicle and I am unable to find any additional leaks. I drive a 1993 GMC G2500 Vandura with a 5.7L V8. Is it normal for the vehicle to run completely fine with the ECT sensor unplugged if there are vacuum leaks?

71,585

Before you unplugged the temperature sensor was your "service engine soon" light on? If so, what code(s) did you get?

1 of 1 people found this helpful.
40

Lean fuel. The exact code was PO44

2 of 2 people found this helpful.
71,585

That could be a bad oxygen sensor, vacuum leak, weak fuel pump, faulty fuel line, EVAP system problem, bad fuel pressure regulator, faulty fuel injector(s), or even a bad gas cap. HTH. -Jim

1 of 1 people found this helpful.
40

O2 sensor replaced, fuel pump checks out as good, fuel injectors cleaned and some vacuum hoses replaced and I'm unable to find any other vacuum leaks.

2 of 2 people found this helpful.
71,585

Is the intake manifold itself possibly leaking? What about the EVAP system?

1 of 1 people found this helpful.
71,585

An exhaust leak, ahead of the oxygen sensor, will cause a code 44. I believe, if I remember correctly, a faulty MAP (manifold absolute pressure) will also make the system go lean as well. HTH. -Jim

2 of 2 people found this helpful.
10

I was having a nightmare with my 1990 gmc 2500 vandura . My engine after driving 1 or 2 miles would start choking and flooding and blowing a puff of black smoke and then shut down. Eventually would start but then do the same thing again if I pressed on the throttle. Well I read your post and thought I have to change the coolant sensor and check all the vacume hoses . Then I see the hose going to the brake booster is actually collapsed just before the booster . Weak old hose . Each time you close the hood it bends at that spot . Thanks for your info . So a leaking hose is just as bad as a collapsed hose . Any input.

1 of 1 people found this helpful.
5

I had same symptoms on 1998 GMC Jimmy. Turned out to be the coolant sensor plug rattling on/off losing contact and causing bucking because of intermittent open connection to computer. P0118 code. You can check by plugging in obd reader and having someone jiggle sensor plug wiring while you monitor coolant temp on the reader. If it switches from -30c (or anything likely incorrect) to the actual coolant or air (if engine cold) temp, you've found the problem.

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