348 Running Challenge...Help!

My normally bullit proof 348 has developed a running issue....

It is fine on start up. After a few miles when coming to a stop (like a traffic light)...the longer it idles....all of a sudden the idle starts to drop and wants to stall. If it doesn't stall, when you hit the gas it sounds and feels like it running on less than 8 cylinders. The car will stumble along and then burst into full 8 cylinders the more gas that you give it.

It happened after a car wash...but I am usually very careful not to get too much H2O in the engine comaprtment.

I have taken MAF connections, and all the coil connections off and cleaned them and put di-electric grease on the connections. THis hasn't helped. I haven't tried resetting the ECU's yet..or checking to see if the plugs are fouled.

The car is an 89 w/the 2.5 system, Tubi/test pipes.

Any ideas? Thanks in advance.

 

Start with the simple things 1st.

Check the fuel pressure regulators. Pull the vacuum hose off of the regs & see if there is fuel in the vacuum hose. That extra fuel would be just dumping into the intake, and causing the symptom you mention. If that is the case, you will need to change the regulator that is leaking (one if not both). Not hard. Very simple.

Next, you may want to change out the coolant temp sensors. They are under the intake and are fairly hard to get to if your not double jointed. They have blue plastic heads on them. Check to be sure the connection is good, or just replace them totally.

02 sensors. You can unplug the 02 sensors & see if that makes any change. They are again easy to change, and not too expensive. If you unplug them & its a noticable change, you may be on to something.

Spark plugs. Good thought. Try some of the new breed of plugs in that 3.4, it may thank you for it even if that is not the issue. Check the plug wires & wire ends. I have heard of a few cars that just needed spark plug wire maintenance.

With the ECU's, I doubt they are the problem. The system is good, and reliable. I have yet to fix a car because I unplugged an ECU for 10 minutes then plugged it back in. But you can try that too.

Dont worry. It sounds like juts a small blip on the radar screen. Nothing a little diagnoses time cant fix.

 

Well pall you have alot of work ahead of you. It really sounds like you have water some place were it doesn't belong. You are going to have to pull off all of the electrical connections and blow them out with some compressed air. You already blew out the MAFS, the next place you need to look is the coils, and the ignitors. Then look at the connections for the throttle position sensors. Unplug them and make sure you don't have any water in them. Have a look at the connectors under, the airbox, for the O2 sensors. Look at the connector on the back of intake cam for the injecton timing. Check the two connectors under the intake plenum for the injectors. In a nut shell you are gonna have to go through everything and make sure there is now water in it. The other thing you can do is use some good ol' WD40 to spray in there. That is what is was made for, to get rid of water were you don't what it. Good luck and keep us posted

 

Thanks for your insight. I don't think this is anything major...just a pain in the butt to figure out.

I'll be off to look through my manuals and locate the regulators...AHHHH! Just found where they are!

What kind of spark plugs are you talking about?

Thanks for your help....Dino

 

The problem turned out to be pretty simple. It was a bad spark plug wire!! I had a spare set and replaced the offending wire and BLAM.....back to normal!!

Thanks...Ciao....Dino

 

Dino,

That's great to hear. Like mentioned I have seen that before, and I am thrilled it was "that easy" to fix.

Maintenance of those plug wires is pretty important.

As for the "new era" of spark plugs... I am having great success with the Denso Iridium plug (I am currently testing part # IXU24). But hold onto your wallet, because they can be upwards of $12 each.

For that kind of coin they should screw themselfs in.

 

I have never heard of that plug!! Where do you get them?

As far as price, I remember paying about that for stock TR plugs....so that doesn't sound that bad.

Thanks for your help..........Dino