Anyone know what would cause me to get a code 34 on about 4 out of 5 cold starts? I know this is a map/ low vac. signal, but i didnt think 2.8's even had a map sensor, if so i've never seen it..

Thanks

 

Scoob,

What year 173 are we talking about? What fuel system - MPFI?

 

my bad, yeah it's a MPFI 87' 2.8

 

With an '87 MPFI, you should have a MAF sensor in the intake tract. The '34' designates a low-flow signal from the MAF. On a TBI or S/D system with a MAP, it is for a low absolute pressure (high vacuum). In your case, the code is definitely MAF, and there could be several reasons for the error code. The DTC '34' is set when the measured intake air is below what is expected at a given engine RPM and throttle position.

First, make sure the MAF has reliable power. There is a fuse on the right inner fender for the MAF unit. Check connections there and at the MAF itself to be sure they are clean and tight.

Make sure the TPS is set correctly and working properly.

Check the intake ductwork between the MAF and the throttle body for leaks, including splits and cracks in the ducts and air boxes.

Make sure the EGR is not leaking.

Check the PCV valve and CCV tube. The crankcase vent tube should be getting its air supply from the throttle body.

Check the condition of the cold start valve air tube and the hose connected to it for leaks or damage.

Make sure your oil filler cap is in place and tight, since any air leaks into the engine that aren't measured by the MAF can trigger the code.

Look for damaged or leaking vacuum hoses, and don't overlook the power brake booster as a possible vacuum leak. Also check the upper and lower plenum halves and the gasketed joints between them.

If you can't find any vacuum leaks and everything is in order, you should test the MAF output to the ECM or scan the ECM with a datalogger to determine if the signal is correct.

I'm guessing that the MAF is not at fault, since the normal failure mode is complete failure with no recovery. You could perform the "tap test" to see if the MAF is reliable. With the engine running warm and in closed loop, gently tap the MAF sensor housing with a screwdriver handle. If the engine stumbles and you get a MIL on the dash, you may have a cracked hot wire in the MAF. The fact that this condition only apparently happens when cold would suggest that you have a different problem, however.

 

found the problem.. at first I thought it was the connection at the MAF, it was missing the rubber weatherpak seal and one terminal had some corrosion on it, cleaned it up and nadda, later checked the fuse holders, cleaned the hell outta em, and nadda, decided to replace the fuse holders, problem fixed.. guess there was just some corrosion down in em I couldnt see.. which one is which? orange/red = maf and red/black = ecm, right?

Thanks

 

So, it was the first item - no MAF power. Make sure you check all the engine grounds as well. If the power connections are failing, the grounds might give you problems in the future.

If I'm correct, the orange wire is the ignition supply, so the red/black is probably MAF load.