• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Poor Gas Mileage, Sputtery idle.

J

jeephick85

NAXJA Forum User
Location
Montreal, Canada
Hi All, I would appreciate a little help. I have searched on here for other peoples similar problems and there seems so be many different possibilities. The problem I have at the moment is poor mileage, a slight hesitation on take off which you can barely feel, and it has a sputtery ( 700 )idle which sound like a slightly misfire. it also doesn't kick down when im going 30 - 40 mph if i give it more gas. If I'm giving it a hard time forcing in the snow and let off the gas suddenly it will sometimes stall out on me. I have changed my plugs and wires ( 35 gap). I did all my vacuum hoses with new hose, have changed my oxygen sensor. I put the scanner and readjusted my TPS sensor, which is at zero and doesn't have a dead spot when tested. Could an intake or manifold leak cause the problem, it also has the catalyser removed.

87 cherokee 4.0
Thanks Alot, Jamie
 
test the egr valve. does it have a slight backfire or miss when you let off the gas pedal?

what do you mean by zero on the tps. i have a manual tranny and when i test the tps, i get just under 5v and the output is set to 83% of that, IIRC. havent done it in a while.

since you have a meter, you may want to spec out all the other sensors. if you dont have the procedures, go to www.lunghd.com search through the on-site tech info for renix sensor diagnostics.

intake leaks will give you a slightly high idle.

sputtering idle could also be a dirty IAC and throttle body
 
Last edited:
89xj said:
test the egr valve. does it have a slight backfire or miss when you let off the gas pedal?

what do you mean by zero on the tps. i have a manual tranny and when i test the tps, i get just under 5v and the output is set to 83% of that, IIRC. havent done it in a while.

since you have a meter, you may want to spec out all the other sensors. if you dont have the procedures, go to www.lunghd.com search through the on-site tech info for renix sensor diagnostics.
Click to expand...

:looney:
 
Ill for sure check out the other sensors. I checked MAF sensor and it was responding properly, and i recall checking most of the other sensor signals and all seemed right. I set the TPS sensor at 0% when it was turned off, ignition on, i misplaced it at one point and it was at 5% and the engine idled to high so I put it back to 0 %. What could cause the tranny not down shifting. Also if im on the highway at 60 MPH its reeving at 1600 in OD and 2300 in 3rd. Automatic trann..
thanks alot, Jamie
 
Forgot to say that it does backfire when its decelerating and it seems to miss when it idles, when its revving it seems to be fine. Jamie 8 miles to the gallon
 
Last edited:
jeephick85 said:
Ill for sure check out the other sensors. I checked MAF sensor and it was responding properly, and i recall checking most of the other sensor signals and all seemed right. I set the TPS sensor at 0% when it was turned off, ignition on, i misplaced it at one point and it was at 5% and the engine idled to high so I put it back to 0 %. What could cause the tranny not down shifting. Also if im on the highway at 60 MPH its reeving at 1600 in OD and 2300 in 3rd. Automatic trann..
thanks alot, Jamie
Click to expand...

Your 87 does not have a MAF sensor....what did you check?
 
Well your RPM's at highway speed seem right to me...were you asking if they were wrong?

Also, you say you've changed the plugs and wires....what about the cap and rotor? Also, check the coil...I had an ignition problem with mine and come to find out, the coil had a crack in it.
 
I didn't change the cap and rotor and I haven't checked the coil either.As I wrote before it only has a smooth idle but it seems to spit and backfires sometime when i release the accelerator. My mileage is at 8 MPG in the city. Also for the tranny what would make it not want to down shift when i press on the gas, I have to floor it to have a down shift when Im going about 30.Thanks
 
Well I wouldn't run right out and buy them...cap and rotor, yeah they're cheap and should be replaced so often anyways since they're so cheap and can cause ignition problems, but I wouldn't run right out and buy a coil without at least checking it first...they're not all that cheap!
 
OK. I changed the Rotor and Cap, Plugs and Wires, checked the TPS for dead spots, Everything was OK. Now that I have changed the Cap and Rotor, I can easily hear it misfiring. I put all the wires back the way they were, and it idles smooth for about the first 2 mins and then it starts to go choppy. The idle goes from 700 to below 500 and the lights dim slightly, but hasn't stalled out yet recently. All I haven't done is change the coil. I know I keep coming back to my tranny shifting at low RPM's (1500). It always seems like its dragging, any time I go up a slight hill I loose speed significantly and if i give it more gas it continues the same and if i push it to the floor it will finally downshift. What is causing this??? I think my ole 85 2.8 had more nuts than my 4.0. at the moment. Thanks Alot Guys. Jamie
 
Your power, shifting and probably the rest of your problems are a bad TPS for sure. It should read about 0.73 volts on the ECU side of the TPS when properly set, positioned. The TCU side of the TPS is definately bad and causing your low rpm/shifting, low power,etc problems. I fought your problem for 2 years on my 87 before I finally figured it out. I have a blow by blow history, with special test methods and data in the "RenX Files" thread here, OEM forum. Go read the last 40 or 50 posts in it. Use advanced search for a title "ReniX Files, use Ecomike for the poster, and OEM forum.

Once again it is the back side, square connector on the TPS that goes to the TCU, Transmission Control Unit that you have not tested, that is bad. And while you are at it, check the ground from both sides of the TPS wiring harness connections to the battery negative post. They seem to go bad too!
 
Last edited:
Thanks Buddy, I remember i checked out the TPS, I know it doesn't have a flat spot and i remember that when i set it the throttle position was at 0% and the voltage was a zero also if I'm not mistaking. Ill go down and get myself a new TPS sensor and hopefully it will be the end of these malfunctions. Will A BAD TPS cause it to misfire?? Thanks alot , Jamie
 
"Will A BAD TPS cause it to misfire??"

YES it can. TPS failure symptoms vary. It can cause a variety of different problems, depends on where it failed, and how.
 
OK just changed the TPS its not zero in yet, now what exactly am I looking for number wise when I adjust it. Right now its on seems to be shifting better but it still has a choppy idle.
 
You must log in or register to reply here.

Similar threads

A
Rough idle & CEL with no codes?
Replies
10
Views
3K
alopeks
A
O
2000 XJ Failed Colorado Emissions high CO
2
Replies
27
Views
2K
Ken M
K
I
High idle, smells like gas, running out of things to replace
Replies
2
Views
2K
Inverhyt
I
D
Temp Gauge Reads High With New Senosr
Replies
15
Views
1K
TheDXJ
T
T
Temp gauge stuck ?
Replies
6
Views
2K
Tonyt22
T
Back
Top