idle drops to 200 rpm after driving 15 mins

[fredcapo]

I was driving my 94 TLC with blown HG over to mechanics garage for HG job. I started loosing antifreeze in December, and realized it was HG and stopped using the vehicle except for occasional 5 minute run. It always ran good, even after i realized i had HG breach, and always had CHECK ENGINE light on. Passed NJ inspection that way.
So today, after 15 minutes i noticed i had to keep on the gas or else it would stall. When I got to mechanics place, it would idle unloaded at around 200 rpm. He is going to dump the codes and see if it is a sensor.

I saw a post about O2 sensors here. What do you guys think is the problem here ? is something shutting down the idle? I would appreciate any info to feed back to the mechanic.

He is doing this job in his home garage - which has a hydraulic lift. Hanging with him for an hour he seems to know his stuff and seems pretty fair.

thanks

 

[CJF]

Seems a little like worrying about a paper cut on your way into heart surgery...

 

[fredcapo]

i disagree

I think, as does my mechanic, that it would be useful to understand and solve this problem prior to starting the HG job in order to understand what other issues need to be dealt with and to evaluate the results of the HG job.

I don't want to be ungrateful, but until now, if appreciated and found most of the information posted here useful or entertaining.

 

[CJF]

I wasn't kidding. Your approach makes no sense to me. The title of your thread is about a low idle, and then your post says, "Oh, by the way, I currently have a blown HG." Any other troubleshooting you do at this point will be suspect, since maybe it's, say, the O2 sensors, or maybe it's a symptom of the BHG. It honestly seems to me like a "Just ignore that big elephant in the corner" approach.

Of course if you like you can search for the usual suspects for a low idle: vacuum leaks, cracked air tube, etc...

Good luck

Curtis

 

[dfmorse]

Be sure battery is in good condition and the connections are clean and tight. Assuming that your mechanic did the head gasket work; he had to disconnect the battery; this dumps the computer. When everything is bolted back together, the engine (ECU computer) will have to re-learn all of its settings. There are a few ways to do this. In your drive way: run engine at 2200 rpm's for about 5 min; or, drive critter down the freeway for 20 minutes.

Mine does this a lot because I'm allways messing with the electrical stuff. I have learned how to use the right foot throddle trick to keep the idle up until my FZJ80 wants to idle at 650 rpm.

...

 

[Rookie2]

I thought one of the symtoms of a blown head gasket, was a rough running engine. I kind of agree that you need to fix the main problem hear first, and then see where that leaves you. So what if an O2 sensor is bad, it's not going to hurt anything to do the HG job and then replace the O2 later if it needs it. I guess what I'm trying to get at is I don't see how your head gasket R&R is going to be any different either way. Be sure to check the head when you get it out to make sure it's not cracked.


Rookie2

 

[CJF]

Assuming that your mechanic did the head gasket work

...

You're missing the point: He hasn't done the headgasket repair yet...

 

[dfmorse]

CJF;

Yea, ur right; I will learn to read someday..

 

[Wilkinson]

A blown head gasket can cause lots of problems. My pickup blew a head gasket and took the O2 sensor with it. And like DFmorse said, if you remove the power from the EFI computer on a 94 it will lose it's mind and take some time before it will idle at the correct speed again.