The Stalling Metro

Dear Roy, The vehicle is a 1990 Geo Metro, and I'm having trouble with poor fuel economy. I rebuilt the engine back in the summer of 2005 with new rings, bearings, 0.020-over pistons and a rebuilt head with new guides and valves.

When I first installed the engine I was getting around 41mpg. Then the first morning that the ambient temperature dropped to around 50°F, it started but didn't go to fast idle, just normal idle speed, and it ran for about 30 seconds, loaded up and shut off.

Since that time I have tried everything in the book but nothing seems to make a difference. I've checked the timing, replaced the engine control module (ECM), oxygen sensor, coolant temperature sensor, manifold absolute pressure (MAP) sensor, checked for vacuum leaks, a plugged catalytic converter, and almost everything that I and several other mechanics could think of. I've checked for codes and everything is normal.

Since the day it got cold, at every cold-start it wants to load up and stall unless I keep the RPMs up. Once the engine warms up, it starts OK without stalling, but the last time I checked it was down to 29 mpg. Please help.

Thanks, Scott Meyers, Millersburg, PA, via e-mail

Dear Mr. Meyers There are a few areas that I would check that I didn't see mentioned in your letter. First and foremost I would check to see that the exhaust gas recirculation (EGR) valve is closing completely. If the valve was sticking or blocked partially open, it could create the symptoms you describe.

I would also test fuel pressure. At idle it should be 13 to 20 psi, and with Key On Engine Off, the pressure should be 23 to 31 psi.

Check the evaporative emissions control (EVAP) system for proper operation and look for a leaking or dirty fuel injector.

Last but not least, take a compression check just to eliminate the possibility of an engine malfunction that may have occurred since the rebuild.

GMC Truck Misfire

Hello Roy,The customer brought this GMC truck in with a complaint of a rough idle. The truck has a 4.3L, 262 CID, six-cylinder OHV gasoline engine with a distributor-breakerless ignition and a four-speed electronic automatic transmission. It has 120,000 miles.

At the first start in the morning, it didn't seem to idle that rough, but the more it ran, the rougher the idle got. The scanner showed a dead miss at idle on cylinder Number Three, but above idle, the misfire goes away.

I checked for a vacuum leak with the smoke machine and found none. Static and running compression tests both appeared OK. The exhaust gas recirculation (EGR) is not leaking and the injector waveform looks good.

I tested ignition components and replaced the plug and tried a different wire. I also checked for a partially clogged injector by adding propane, and because the idle seemed to im prove slightly, I installed a new injector. But there was no improvement.

Next I looked at the camshaft position sensor (CMP) retard and found it to be retarded by nine degrees. I ground the locking tab off the distributor to make timing adjustable and reset it to zero.

After looking at some posts on iATN, I saw there were a lot of problems with lifters. One tech suggested removing the valve cover and loosening rocker arms to see if the idle smoothed out. I did this and the engine came back to a steady idle. I replaced all the lifters, put the engine back together and the same symptoms returned.

Is there something I'm missing here? What else could it be if I loosen the rockers and the engine smoothes out? Have there been a lot of valve problems on these 4.3L engines? Any help or suggestion is appreciated.

Chuck Hoffmann, Wittlin's Service Menomonee Falls, WI

Dear Mr. Hoffman:In as much as the engine runs well with the rockers loosened, the problem would seem to indicate a mechanical malfunction. Has anyone done any head work on this engine? Are all the valve stems the same height? A valve could be seated too deeply or a valve head may have tuliped.

Are the pushrods correct for the engine? Are the valve springs in good condition? Is the oil pressure within specifications?

A careful check of these areas should produce the answer to your problem.

The Whistling Jeep

Dear Roy, I have a 2002 Jeep Grand Cherokee with a 4.0L engine and a 46RE automatic transmission. There is a shrill whistling sound coming from the engine only on deceleration. The engine must be run through a warm-up procedure before the noise will occur, and as it reaches operating temperature, the whistling noise becomes very loud and shrill. It seems to be centered around the throttle body.

There are no obvious vacuum leaks. The throttle body gasket is intact and the throttle body has been inspected for warp, wear, etc. The problem is further complicated because this cannot be duplicated by allowing the engine to warm up at idle in the service bay.

Furthermore, this noise will dissipate once the engine has returned to idle. The noise wanes as the tech is attempting to diagnose the problem and will not recur until the engine is cold and is run through a warm-up procedure again.

The customer has had some service work done, including an updated fan clutch. This noise is not emanating from the front of the engine.

Any clues? Charles McCormick, Manager/ASE Master Tech Automatic Transmission Design Germantown, WI

Dear Mr. McCormick Sure sounds like a vacuum leak. The fact that the noise is sporadic, leads me to believe the leak is the result of something that can move or change as compared to a fixed vacuum leak.

Have you thoroughly examined the IAC and the PCV Systems? How about the power brake booster system? Does this system have a leak detection pump? If all these check out, make sure that no one has been fooling with the throttle stop screw on the throttle body.