Rich and rough idle
#1
07-24-2018, 06:09 PM
Join Date: Jul 2018
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Rich and rough idle
Hey all,
I have a 98 Dakota V6. The only issue I can't sort out is the idle. It idles very rich and at about 500 RPM in closed loop. Runs fairly well open loop, but a little erratic. It accelerates and cruises just fine. Plugs were clean. MPG is a little weak...about 13.5 city, 16 Hwy
1. Changed IACV
2. changed both O2 sensors
3. TPS was changed just before I bought it.
4. changed plugs, wires, cap and rotor. (OEM Champion plugs)
5. Just had new Cat installed (old was rattling)
6. Does not trigger a fault (no Check Engine light)
7. I also checked every vacuum accessory for leaks. I even pulled every vacuum hose off the TB and manifold and plugged the ports. I did a crankcase pressure test, and the blow-by pressure builds up when PVC is plugged. Intake manifold and TB are not leaking, no pooling oil in the plenum.
8. Lastly, I pulled the air temp sensor, and I got ohms changing widely from freezer to a hot air gun.(don't remember the values)
Anyone else have this issue? None of these items improved the vehicle performance, nor did it hinder anything. Truck has 105,000 miles and is in very good condition. I might also add thet the idle will hunt, not a steady 500, but it moves up and down about 100-300 RPM about 1/2 -1 second cycles.
Thanks for reading!
Andy
I have a 98 Dakota V6. The only issue I can't sort out is the idle. It idles very rich and at about 500 RPM in closed loop. Runs fairly well open loop, but a little erratic. It accelerates and cruises just fine. Plugs were clean. MPG is a little weak...about 13.5 city, 16 Hwy
1. Changed IACV
2. changed both O2 sensors
3. TPS was changed just before I bought it.
4. changed plugs, wires, cap and rotor. (OEM Champion plugs)
5. Just had new Cat installed (old was rattling)
6. Does not trigger a fault (no Check Engine light)
7. I also checked every vacuum accessory for leaks. I even pulled every vacuum hose off the TB and manifold and plugged the ports. I did a crankcase pressure test, and the blow-by pressure builds up when PVC is plugged. Intake manifold and TB are not leaking, no pooling oil in the plenum.
8. Lastly, I pulled the air temp sensor, and I got ohms changing widely from freezer to a hot air gun.(don't remember the values)
Anyone else have this issue? None of these items improved the vehicle performance, nor did it hinder anything. Truck has 105,000 miles and is in very good condition. I might also add thet the idle will hunt, not a steady 500, but it moves up and down about 100-300 RPM about 1/2 -1 second cycles.
Thanks for reading!
Andy
Last edited by restlessswind; 07-24-2018 at 07:18 PM.
#2
07-26-2018, 06:25 PM
I also have a 1998 Dakota with the 3.9L V6, had a similar problem, although ontop of, it would give me a false misfire code. The main issue for me was the Crank Position sensor found on the back of the block on the passenger side bellhousing. It caused a random lope in my idle (twice it actually stalled), and if I went over 65, it'd set codes 300, 301, 303, and 305 (although usually only one of them, rarely more than 2, and not all the time). At this time, cruising had no issues and plenty of power. My gas mileage was about as you say yours is. Normally first would be the IAC, but you've already checked that. O2 sensors, hopefully you went with either NTK or Denso, these trucks hate Bosch. Plugs, champions are not that great, test a set of cheap copper core autolites, these old style motors seem to love 'em. Bonus on the autolite plugs is get the 3923, they're a heat range cooler and they're not the extended tip, which helps with heat control and prevent pinging. The stock autolites are 5224. Personally, I'm running NGK FR5-1 V-Power, which is stock in NGK.
The crank and cam sensors control the fuel sync. Cam tells the pcm where the spark is, crank tells the pcm where and what speed the engine is, these being sluggish can cause all sorts of problems. Cam sensor you can get away with a good 3rd party (I have a Standard brand) it's under the dist cap. The crank sensor you want OEM (I pulled mine from a junkyard for $4). My MPG has gone up to constant 18-19. Easiest way to get to the crank sensor is jack the front of the truck up, remove the passenger front tire, pull back the back of the fender liner and look behind the exhaust manifold. You'll see two hex bolts holding the sensor on, the harness goes up behind the dist. a 10mm socket + 1/4" drive ratchet is easy enough. Hit a junkyard for cheap parts first, you can pull these two sensors from any 3.9 V6, 5.2 V8, or 5.9 V8 from a Dakota, Ram 1500, or Durango. Careful with the crank sensor rubber grommet, lubricate it with something like a bit of oil or lithium grease so the sensor slips in smoothly and sits correctly. If you don't it might not let you push the sensor in correctly and after bolting it down, will have it at an angle where the flexplate can eat the end of the sensor.
The crank and cam sensors control the fuel sync. Cam tells the pcm where the spark is, crank tells the pcm where and what speed the engine is, these being sluggish can cause all sorts of problems. Cam sensor you can get away with a good 3rd party (I have a Standard brand) it's under the dist cap. The crank sensor you want OEM (I pulled mine from a junkyard for $4). My MPG has gone up to constant 18-19. Easiest way to get to the crank sensor is jack the front of the truck up, remove the passenger front tire, pull back the back of the fender liner and look behind the exhaust manifold. You'll see two hex bolts holding the sensor on, the harness goes up behind the dist. a 10mm socket + 1/4" drive ratchet is easy enough. Hit a junkyard for cheap parts first, you can pull these two sensors from any 3.9 V6, 5.2 V8, or 5.9 V8 from a Dakota, Ram 1500, or Durango. Careful with the crank sensor rubber grommet, lubricate it with something like a bit of oil or lithium grease so the sensor slips in smoothly and sits correctly. If you don't it might not let you push the sensor in correctly and after bolting it down, will have it at an angle where the flexplate can eat the end of the sensor.
#3
07-27-2018, 12:25 PM
Join Date: Jul 2018
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Thank you! I will try the Crank sensor next. I'll check my local pick'n'pulls. Yeah, I get no codes ever. I did buy Denso O2 sensors. The new cat did clean up a lot of the fuel smell and the annoying rattle that everyone in the intersection could hear. There is never a misfire, ping or hesitation. Just a constantly self-adjusting slow idle. When fully warmed up, it idles at 550-600 rpm (dash tach), as I add a little throttle, the 50 rpm variance spreads to about 100 rpm until the engine hits about 1500rpm, then it smooths out. Even in gear, the truck pulses at idle while rolling. It only seems to stall sometimes right after I start a warm engine and put it in gear, and try to take off smoothly. I usually need to rev it before putting it into gear and jump into cruise fairly quickly. Running the A/C doesn't seem to have any effect on the idle behavior.
I also have a 1998 Dakota with the 3.9L V6, had a similar problem, although ontop of, it would give me a false misfire code. The main issue for me was the Crank Position sensor found on the back of the block on the passenger side bellhousing. It caused a random lope in my idle (twice it actually stalled), and if I went over 65, it'd set codes 300, 301, 303, and 305 (although usually only one of them, rarely more than 2, and not all the time). At this time, cruising had no issues and plenty of power. My gas mileage was about as you say yours is. Normally first would be the IAC, but you've already checked that. O2 sensors, hopefully you went with either NTK or Denso, these trucks hate Bosch. Plugs, champions are not that great, test a set of cheap copper core autolites, these old style motors seem to love 'em. Bonus on the autolite plugs is get the 3923, they're a heat range cooler and they're not the extended tip, which helps with heat control and prevent pinging. The stock autolites are 5224. Personally, I'm running NGK FR5-1 V-Power, which is stock in NGK.
The crank and cam sensors control the fuel sync. Cam tells the pcm where the spark is, crank tells the pcm where and what speed the engine is, these being sluggish can cause all sorts of problems. Cam sensor you can get away with a good 3rd party (I have a Standard brand) it's under the dist cap. The crank sensor you want OEM (I pulled mine from a junkyard for $4). My MPG has gone up to constant 18-19. Easiest way to get to the crank sensor is jack the front of the truck up, remove the passenger front tire, pull back the back of the fender liner and look behind the exhaust manifold. You'll see two hex bolts holding the sensor on, the harness goes up behind the dist. a 10mm socket + 1/4" drive ratchet is easy enough. Hit a junkyard for cheap parts first, you can pull these two sensors from any 3.9 V6, 5.2 V8, or 5.9 V8 from a Dakota, Ram 1500, or Durango. Careful with the crank sensor rubber grommet, lubricate it with something like a bit of oil or lithium grease so the sensor slips in smoothly and sits correctly. If you don't it might not let you push the sensor in correctly and after bolting it down, will have it at an angle where the flexplate can eat the end of the sensor.
The crank and cam sensors control the fuel sync. Cam tells the pcm where the spark is, crank tells the pcm where and what speed the engine is, these being sluggish can cause all sorts of problems. Cam sensor you can get away with a good 3rd party (I have a Standard brand) it's under the dist cap. The crank sensor you want OEM (I pulled mine from a junkyard for $4). My MPG has gone up to constant 18-19. Easiest way to get to the crank sensor is jack the front of the truck up, remove the passenger front tire, pull back the back of the fender liner and look behind the exhaust manifold. You'll see two hex bolts holding the sensor on, the harness goes up behind the dist. a 10mm socket + 1/4" drive ratchet is easy enough. Hit a junkyard for cheap parts first, you can pull these two sensors from any 3.9 V6, 5.2 V8, or 5.9 V8 from a Dakota, Ram 1500, or Durango. Careful with the crank sensor rubber grommet, lubricate it with something like a bit of oil or lithium grease so the sensor slips in smoothly and sits correctly. If you don't it might not let you push the sensor in correctly and after bolting it down, will have it at an angle where the flexplate can eat the end of the sensor.