I'm having this problem that is intermittent. Happens a lot after braking in reverse. The engine will almost stall like it has a loss of vacuum. When this happens if I stop and idle the engine, it runs rough. The belt will chirp a bit at this time. The engine will then have almost no power and doesn't respond normally to acceleration. Sometimes it backfires a few times. Eventually it will all of a sudden kick in and have a power surge and take off. Seems to happen a lot on hills. If I turn the ignition off and then restart the engine, everything is fine again. I changed the cap and rotor and checked the map sensor which gives 4.58 volts when I back probe the sensor. The other day it also would rev up and go back down repeatedly at idle. I punched and released the pedal and it stopped. I have a few other problems which may or may not be related but I'll start with this. Any ideas what is going on? Thanks!

 

With the ignition on but engine not running you should have 4.5 to 5 volts on the center wire of the MAP sensor. Leave your probe connected on the center wire, start the engine and let it idle, the voltage should steadily drop to somewhere between 1.3 and 2 volts. Anything higher or lower is an indication the MAP sensor could be bad.

This problem could also be a bad and/or dirty Idle Air Control Valve. It is located on the back of the throttle body and it's pretty easy to remove and clean it. Use a shop rag soaked in throttle body cleaner spray and clean the black crusty crud off the pintle end. Spray the shaft and work it in and out a few times, when you go to re-install it, try to leave the shaft in the same position it was in when you removed the IAC. Lube the o-ring with clean motor oil when you reinstall the IAC. Also clean the orifice and mounting area on the back of the throttle body.

Backfiring could be any number of things. If you still have the original O2's this could be a good time to change them out of you have more than about 80,000 miles on your truck. O2's can get lazy but still not set a trouble code. If there are no trouble codes stored you might want to take a look at the O2's. You can check for codes by turning the ignition from on to off, on to off again, on one more time and leave it on. Any codes you have stored will display in the odometer window. If there are multiple codes it will say "P Done" after the last code is displayed. You can find explanations of the codes in the FAQ section at the top of our Second Gen page.

My guess on this one is a bad IAC, especially if it has never been cleaned or replaced.

Jimmy

 

Thanks Jimmy! I will try cleaning the IAC and see if that helps. The bank 2 number 2 O2 sensor was giving an overvoltage or shorted code a while back. I found a few cracked vacuum lines and fixed them, fiddled with the wires, deleted the code and the error went away. There are presently no codes.
Yesterday we had a crazy rain storm and when I started the truck the belt started squealing and the engine was losing power and backfiring on acceleration. When the belt finally dried out and stopped squealing acceleration returned but now when city driving and going very slow and letting off the accelerator, it wants to die but then idle picks up again.
The belt has been squealing a lot at start up lately. I suspect dry bearings on the belt tensioner pulley. Usually when acceleration is poor, the belt chirps. Could a slipping belt cause the poor acceleration and backfiring? Thanks!

 

Ok, the map sensor checks out ok. Took the IAC off today to clean it. The rod seemed stuck and wouldn't go in or out. After cleaning I managed to get it to move. Pushed it in and when trying to pull it out it came off. Put it back together and worked it in and out a bit and stuck it back on. At first it did the same thing with loss of power and backfiring but started to work better after a while. I think I need to change the IAC for sure. Not sure if that is the whole problem. If not I guess I will try the O2 sensors.

What about a clogged catalytic converter? How would I check for that?

 

A new IAC is not expensive, probably about $40.00 at most any parts store. I would not use the old one if it broke apart like that, better to replace it with new and drive the truck a few miles to let the PCM learn the new IAC. You can check the cat by smacking it with your fist. If it rattles or sounds like it has marbles in it then it is bad. I don't think your problem is a bad cat. If the cat was bad you would have the power loss problems all the time, not just when accelerating or only in rainy weather.

The tensioner has marks on it that you can look at while the engine is running, they are supposed to let you know if the tensioner is bad by whether the tensioner moves past the marks during operation. I never relied on that, I just moved the tensioner by hand (withe the engine off). If it moves more than 1/2" or so it might be best to replace it. Remove the belt and spin the pulley by hand. It should be smooth and quiet, if not you can replace the pulley, but if it were mine I would just replace the entire tensioner as a unit. I replaced my own tensioner about a year ago (for the second time). I replaced my OEM tensioner when I bought my truck used with 42K miles. The belt was squealing and it kept slinging off the pulleys when I would start the truck. A new belt and tensioner fixed the problem. I bought the new tensioner at Napa, it cost about $85.00. This last time I replaced my tensioner with one from RockAuto.com. It only cost $29.95 plus a few bucks shipping and is the exact same part as the Napa tensioner. You need to either use Napa, Rock or an OEM tensioner, the ones they sell at Autozone and Advance are not built the same and will cause problems. I bought and returned 2 tensioners at Auto Zone before I figured that one out. I personally don't know for sure but I would guess a bad tensioner and belt problems from wet weather could cause power problems if the belt can not turn normally.

I still think this problem is a bad IAC. Let us know how it turns out.

Jimmy

 

I am waiting for the part to come in the mail. Napa was $105.00 and other places not much cheaper so I bought off of ebay at like $32 something shipped. It's coming from California so it will take awhile. Hope it's a good one.

In the meantime, I'm wondering if there could be other causes. I first suspected the distributor pickup. Now I'm wondering about something else. I recently changed the rusted out muffler for a smaller in size thrush muffler. It had the 2.5 inlet and outlet, but could the wrong size muffler cause this problem? Some automotive sites online showed it as ok for this model dakota, but I'm wondering about it. Any thoughts?

 

I don't know a lot about exhaust but I have read the factory exhaust is just this side of restrictive. A lot of Dakota guys have changed out their exhaust, gutted the cats, etc for better performance. Personally I would only use a direct replacement muffler, I don't think it would be good to go smaller. Is that when the backfiring started? Others here may chime in with more info on the muffler. What part was it that cost $105.00?

Jimmy

 

An OEM muffler is a big beast and OK but there are many better mufflers on the market but I don't chose my mufflers for making my truck sound cool I like quiet and OEM is good for that.

Having the 2.5 engine getting anything would work for me but I put a Flowmaster 40 or 50 on it and it was a bit louder than stock a nice low rumble almost too loud for me.

Funny but most people recognize my truck by its sound before seeing it.

You may have put the wrong muffler on it

 

I'm not exactly sure if the backfiring started before or after, but it is definitely worse than before. I kinda think (like you said about the cat) that if it was the muffler it would do it all the time. Maybe I'm wrong about that.The $105.00 part is the IAC at Napa (Canada).



You're right about that. I'll see if I can find the one I put on and post it.

 

It's a thrush turbo model 17715. It's supposed to decrease backflow by 30% and is a reversible universal fit. Autozone will say it is the wrong model but the one they say is the right one is exactly the same except both inlet and outlet are offset while on mine one is centered. I did have to angle it a bit to make it fit but it fits fine. From all I can tell this shouldn't be the problem. What do you think?