Need advice.. Truck starts great and runs around 800rpm idle, noticed a slight surge to 900-1000rpm when sitting. Whenever accelerating though it feels hesistant and sluggish and than catches itself.. It happens about 80% of the time, whenever i stop and accelerate. Only two things that come to mind is the tps is bad or the fuel filter/pump is bad. Any thoughts? Thanks.

 

I've also noticed a hissing noise coming from the engine whenever i accelerate but noticed the air filter housing isnt completely clamped onto the throttle body and thinking this could be the cause

 

could be a few things. what maintenance has been done to the vehicle? plugs, wires, cap, rotor, filters? have you read up on the plenum gasket failure? hissing sound could be a vacuum leak, but the rpm's are a bit low for anything dramatic. plus vacuum leaks tend to get quieter when revving the engine.

i guess my point is, how many miles does it have and what is the maintenence history. troubleshooting something with 50,000 miles and perfect maintenance is different then noobie just bought a truck from a tweeker with 160k and no idea whats going on other than finding drugs in the visor and ratchet straps with c clamps on the rear suspension. that last part was me btw lol.

 

172k miles, i bought it at this and have only recently been able to get it running good.. Before it had a surging idle/stall at every stop light/sign before i found the o2 sensor was the culprit

- iac valve (replaced)
- spark plugs and wires (replaced)
- coolant temp sensor (replaced)
- starter (replaced)
- throttle body (removed and cleaned, about 95% of the gunk came off)
- upstream o2 sensor (replaced)

 

good so far... i'm still leaning toward ignition. did you check the cap and rotor when you did the plugs and wires?

have you checked the air filter? make sure the vacuum lines are attached and not rotten/cracked? maintenance items usually resolve most problems, if it's still there after the normal maintenance is caught up then theres an actual problem. the plenum gasket is usually the first actual problem.

https://dodgeforum.com/forum/2nd-gen...um-thread.html

 

I didn't check the cap and rotor no, i can replace them and see if that fixes it.. Air filter i held up to sunlight and could see through but it probably does need a replacement. While im at it ill remove the vacuum hoses and check for any leaks. Should i go ahead and do the test listed under that other thread for oil pooling in the intake?

 

Only thing is wouldn't i have engine misfires or failing to start if the cap and rotor were failing?

 

Maybe.

Yeah, check the plenum while you are in there. Unstable idle usually is an indicator of a vacuum leak.... and the plenum is a great place to have one, that can be difficult to find.

 

eventually, at first it would just seem to be running a bit rough/stumbly and as a result your idle would bounce around a bit. cap and rotor wear gradually like brakes. i've seen a new set crack after water splashed on them from going through a deep puddle. carbon can build up inside and cause crossfire/shorting even if the terminals are fine. honestly, unless you're using top notch unobtainium parts you should just change them with your plugs and wires.

it could also be a vacuum leak, but in my experience the idle rpm is usually higher with a leak bad enough to cause driveability issues. like 12-1500 or even higher, depends on how much air is leaking. the leaks can also vary with engine temp because of the metal expanding making it worse or better.

every magnum should get checked for that plenum leak.

 

Didn't have much time to fiddle with it today, got off work late but i wanted to rule out tps entirely so i tested the wires with my multimeter and showed everything to be getting correct voltage (didn't back probe it though).. So i unplugged the tps and drove it around the block and the rpm got so low it actually lost power and stalled twice when giving it acceleration from a stop. I also noticed i had a dripping coolant leak coming from the coolant temp sensor i replaced. From where the nut is to tighten the sensor i can actually fit two quarters in the gap which doesnt seem good but i had fears of tightening it down too tight and risk breaking it since i heard it was fragile. Not sure if this could cause the issues im running into? Im still going to replace the cap and rotor like you suggested, just thought i should offer some info on what i managed to check with what daylight i had left.