Brian68

Hello everyone! I've got a problem I can't figure out. I have a 94 V6 that when the defrost (front not rear) or mix is on the engine surges. It's like your giving it gas to rev it up and it's pretty rythmic (not sporatic). Before I realized it had something to do with the defrost I replaced the AIC valve thinking that was the problem. If it's in anything but defrost or mix this doesnt happen weather idleing or driving. I checked around the engine and didn't see any vaccume hoses that have come apart, but there are a few that have started to crack that might be leaking. I tried pulling them off and putting them back on one by one with no difference. I wouldn't think it's anything electrical or it wouldn't be isolated to the defrost. I just cant figure this out and any help would be appreciated.

Thanks
Brian

projectresto83

Disconnect the A/C compressor and see if it still happens. When you have it on MIX or DEFROST the A/C is also engaged. The extra load can cause the motor to surge if the pump is starting to seize because it pulls so much of an extra load.

shipwreck_98

Your alternator is is producing more voltage which causes a drag on the engine. Its usually a sign that it is about to fail. You should get that tested, they can do it free at autozone or advance auto.
Or your blower motor has a huge drag on it, high resistance, drawing more voltage than is necessary. You can do a resistance check on your motor and leads.

Derf00

+1 , but rather than disconnecting the A/C try to turn it 'on' and see if its the same issue. If it is, then you know it's AC/Compressor related.

Brian68

You guys are totally awsome! I totally forgot about the a/c kicking on in defrost mode and I never checked it in a/c mode as it's winter here. I feel like such a dumb a$$. Cool...I'll check the a/c compressor and the alternator and let everyone know how it goes.

Hey Projectrestro83 where in Indiana ya from? I'm in Indy.

projectresto83

During the winter you should just unplug the a/c compressor anyway........



I'm from New Castle.....40 mile drive down 70E

Brian68

Ok...I've got an update. I unpluged the A/C and that partially worked. When going from anything to A/C, Max A/C, Defrost or mix it will surge once and the voltage guage jumps. This happens only once when the switch is turned and not again. Any ideas?

projectresto83

If it gives you just the one surge its nothing to really worry about. Your charging system is just catching up to the need. It could indicate a weak alternator BUT that alt could last you years or days. I would just leave the A/C unplugged and go about your business as usual.

Brian68

Update!
I'm still having some issues. With the A/C unplugged the surge is gone with the exception of the one time it's turned on, but now the idle stay high while driving. I've changed the IAC valve and the EGR valve thinking that was the problem, but no luck. I've plugged the A/C back in and the idle doesn't stay high, but it is still doing the surging thing. While it's surging I hear a "sucking" noise like it's got a vacuum leak. The sound is coming from somewhere under the IAC valve or throttle body. If it was a vacuum leak wouldn't it be constant and not just when it's surging. Anybody have any ideas? I can post videos of the sound etc if that'll help.

Thanks in advance.

projectresto83

post it....

Where in Indiana are you from?