AC Warm At Low Rpm

Cons Santos’s question:

” Just recently my AC evaporator has a leak and has been replaced by a technician with a new evaporator. However, during engine idle(RPM 1000), cooling is poor while during high RPM 1500 and Up, cooling improved significantly. I hope you have a suggestion on what to do next. Thanks.”


It could be a few things doing that. One, he just might not have put the correct amount of refrigerant in. Two, he may not have changed out the AC drier, in which case the system wouldn’t flow right at low speeds ( ALWAYS change the drier when the system is opened up.) Three, it could be a cheaper aftermarket evaporator which just won’t work as well because the cooling tubes inside it are too small, I see that a lot with cheaper Chinese made replacement evaporators. These are the three most common mistakes people make when working on an AC system that would cause your exact problem. Good Luck,

85 Nissan 300zx reverse light wont turn on when i put the car in reverse

Jimmy Alvarez’s question:

” I have a 85 Nissan 300zx and for some reason the reverse light wont turn on when i put the car in reverse and that’s the only thing that wont let me pass the emissions test i already changed the bulbs but no results…what can i do?!?!?”


Well, 99 percent of the time it’s the back up light switch on your transmission that’s gone bad. Generally the only place that sells such a part is the dealer, so go there and they can sell you one and show you on their computer where the switch is on the transmission. If that doesn’t fix it, then either the wiring has a short in it or the piece inside the transmission that turns the switch on when you go into reverse would be broken (rather rare, but I’ve seen it happen.) Normally though, it’s just the switch on the transmission gone bad.

1998 Chevy Malibu makes a clunk when I go over larger bumps.

Oliver’s question:

” My 1998 Chevy Malibu makes a clunk when I go over larger bumps. A shop changed out the strut mounts, the torsion bar bushings, and the front struts. But the clunk is still there. I took it back and they said nothing was loose now. Have you ever seen this before?”


Well, as a matter of fact, I was stung by this very same problem last year. It turned out that the outer tie rods were making the clunking noise–even though they had no play in them when pulled on, and physically looked perfectly OK. It’s a rare one, but it happenned to a Malibu I was working on, and it took me a while to figure that out. As tie rod ends are pretty inexpensive, you might try that next.

2002 VW Beetle is pinging and has poor acceleration. Code 17536 for long term fuel trim lean

Jeremie’s question:

” My 2002 New Beetle is pinging and has poor acceleration. It has code 17536 for long term fuel trim lean. People are trying to sell me all kinds of stuff for hundreds and hundreds of dollars. What do you think I should do?”


Well, before you spend a bunch of dough, I’d advise changing out the main fuel filter and cleaning the Mass Airflow Sensor (or MAF.) VWs are notorious for getting crud on the MAF sensor and then running lean. And fuel filters do clog up over time and when they do, not enough gas can make it to the injectors, so the engine can run lean. I’ve cleaned lots of VW maf sensors to get them running normal again, it’s a pretty common problem. so try that before spending a bunch on parts you may not need. And if you do need a new MAF sensor because the old one is just plain worn out electronically, you can purchase a quality remanufactured unit instead of the VERY expensive VW OEM new sensor.

2004 Chevy Tahoe’s AC compressor won’t come on and stay on

Nat’s question:

” My 2004 Tahoe’s AC compressor blew last week. So I installed a new compressor and drier and orifice tube. But the AC won’t come on and stay on. Help me!”


Well, you might get a really quick and easy fix here. Those AC systems are all computerised these days, and as many computers are, they need resetting when a problem arises. Simply disconnect your battery for five minutes. Then connect the terminals back on and start up the engine. I’ll bet it starts working then. That happenned to me once and nearly drove me to the looney bin until I figured it out.

1994 Pontiac Trans Sport minvan hard start

Arleen Ramos’s question:

” Hi . Can you please help? We have a 1994 Pontiac Transport minnie van. It has always started on the 1st turn but lately it has to turn several times befor it starts. I know it’s not the altinator and it has a new battery, plugs and wires. It’s taking longer and longer to start. Also it has plenty of get up and go. It’s just starting it. Thank You Very much and God Bless You for taking the time.”


Well, old age is catching up with your Transport (as it does to us all.) From your symptoms, you would have a problem in the fuel injection system. If you remember the olden days, we used to pump the accelerator on old carbureted vehicles to squirt gas into the carburetor. That would get it to start. In modern cars, this is done automatically by the fuel injection system WITHOUT having to pump the accelerator. So first, try pumping your accelerator a little as you crank the engine. If it starts right up then, you have a minor fuel injection warm up system problem. If you don’t care, you can start the vehicle that way ( I have MANY customers who have done this over the years.) If you do want to discover what’s wrong, it can get REALLY expensive and time consuming for such a minor problem if it starts with pumping. You would have to have the fuel pump checked for proper pressure and volume, you’d have to have the computer warm up circuits checked for proper operation, you’d have to get the fuel injectors themselves checked out, and you’d also have to check the entire warm up system wiring and sensors. BUT, as a wild guess, the pump could be starting to wear, so you might try changing the fuel filter first and have a test done on the fuel pump itself. I have seen pumps starting to go out act like that (they don’t work right when starting cold, but once they start pumping they work fine until they cool off again–pumps sometimes will break in this fashion.)


George’s question:



those old 6 cylinder benzes generally all burn a lot of engine oil as they age due to their poor valve design. So first, pull out the spark plugs and see what they look like. If they’re all burned and covered with black crud, that’s burned oil. Replace them and see what happens (and realize if the plugs are really clogged that the engine is just plain wearing out.) Now if you put in new plugs and it still stalls out, then odds are you have a fuel system problem. Have the fuel pump pressure and volume tested to see if it’s wearing out. That old fuel injection system is a mechanical system, and if the fuel pressure isn’t exact, it won’t run worth beans. The mechanical fuel injection distributor under the air filter will also often get clogged up and may need to be taken apart and cleaned (only a good mechanic should ever try that, they are VERY touchy about correct settings.) You must realize that your car has mechanical (not electrical) fuel injectors which operate like inverted bicycle tire valves. ANY dirt or corrosion wrecks havoc with them,and they will not operate correctly without the exact pressure that they were designed for. Good Luck,

2003 ford expedition moisture on spark plugs

Carrisa Smith’s question:

” I drive a 2003 ford expedition. We have replaced spark plugs and a mechanic told us somehow we are getting moisture in them. We have cleaned out the converters. The car is misfiring and is getting bad gas milage. Can you help.”


Generally, if you get moisture on your spark plugs, that moisture is antifreeze from your cooling system. This means that either the head gasket on the engine is starting to blow, or the intake manifold gasket is starting to go and coolant is getting sucked into the engine. Unfortunately, you will have to take the engine apart to discover where the problem lies. BUT, here’s a test you can have a mechanic perform. Have them pressure test your cooling system. If the pressure is lost quickly, then the intake manifold leaking could be the problem (assume you don’t see leaks anywhere else when it’s pressurized.) If you don’t lose pressure quickly, then odds are it’s the head gasket that’s starting to blow, as you won’t lose pressure quickly if a head gasket is starting to go. Hopefully it’s the intake, as that’s a MUCH cheaper job than a head gasket. Good Luck,

1999 Chevrolet Prizm MIL light on all the time

Peter’s question:

” Hi , I drive a 1999 Chevrolet Prizm. It has MIL on all the time. There is a code: PO420. Where is the problem? I am seeking your advice. Thank you. Regards, Peter”


OK, PO420 is the code for catalytic converter low efficiency. There are three possible causes: a bad catalytic converter, bad wiring, or bad oxygen sensors. THE most common problem is a weak catalytic converter, but pinpointing if this is your problem is rather hard. The oxygen sensors give feedback to the main computer about how the cat itself is working, and PO420 sets if the computer decides the cat is bad using this information. This is a very complex algorism in the computer software, and checking can be done by a professional mechanic indirectly using an oscilliscope. Since this costs a ton, and isn’t always completely accurate, you might just try replacing the rear oxygen sensor (the one after the cat.) It is the cheapest part in the system and a bad rear sensor can trip that code. Now if that doesn’t do it, a new aftermarket cat could be welded on your Prism, which would save you hundreds over the cost of an OEM cat. But it’s still going to cost you two to three hundred dollars for that guess. So I’d try the rear oxygen sensor first if you want to take a stab at it. BUT, on the plus side, an inefficient cat code really isn’t going to make your Prism run any different. It will just make your car fail the yearly state inspection if your area does emissions testing.

2004 Mitsubishi brakes pulse

Allen’s question:

My 2004 Mitsubishi has brakes that pulse when I stop fast. I thought it was the brake rotors being warped, so I changed the brake pads and rotors out. But it’s still pulsing. What could it be?”


Well, that normally will fix such a problem, but since it didn’t in your case, here’s the two other common possibilities. First, you could have rust or debris on the hub, so when you put the new rotors on, they aren’t sitting flat. This is called Run Out, and it will cause brake pulsing. And second, make sure the pins on both brake callipers are properly lubricated and aren’t binding, because if they are binding, you will get pulsation. If those two pins on each side can’t slide back and forth smoothly, the brakes will pulse on fast stops.