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Rough idle at dead stop only and P0135 and P0155 codes

Echo5

Member
Supporting Member
Aug 18, 2018
55
Eastern PA
2002 Sahara manual, ~142000 miles, no codes reported

Last week when I pulled into a parking spot the issue started - my idle would drop to the point of almost stalling. The issues persisted and I diagnosed as best I could finding that the low idle only occurred at a complete stop but if I tried to gas the engine slightly (at idle) it would stall. Cruising at idle presents no drop in RPMs to match what is happening at a dead stop. I believe the IAC needs some cleaning and I plan on doing that ASAP.

However, this morning I had to move the Jeep from my driveway to the garage and it stalled hard. I was able to restart the engine but only by applying gas while cranking the engine. After some fancy stick/gas/ebrake work I was able to get into the garage stalling about 3 more times. This is where it gets weird - once in the garage it did not stall (I expected to have to coast in) and idle seemed normal. I did not have time to play around as I did not have time.

I do have a bluetooth OBD dongle that I will hookup to see if anything weird is reported, but 2002 doesn't seem to be new enough to give super awesome data.

Besides cleaning the IAC is there anything I should be looking for/at? Thanks!
 

Quigley

Member
Oct 20, 2018
70
Kingston, WA
I would start by taking off and cleaning the throttle body as well as the IAC. Its free and might be the issue.

I had something similar happen to me and through parts at it 😁 No codes and running like poo.
 
OP
Echo5

Echo5

Member
Supporting Member
Aug 18, 2018
55
Eastern PA
Pulled the IAC this morning. Not very dirty, nothing compared to @Chris pictured IAC. Cleaned it and the housing for good measure. No improvement.

Hooked up the bluetooth OBD reader using OBD Fusion on the iPhone and got no codes, but it did report pending codes of P0135 and P0155. I did some quick Google-fu and these codes *may* not be related. However I have not troubleshot this at non-operating temperatures and found that my Jeep will stall in short order when idling after startup.

So, what parts do I start throwing at this thing? New IAC? I figure new O2 sensors are just a good investment.
 

Chris

Administrator
Staff Member
Sep 28, 2015
37,147
Salem, Oregon
Pulled the IAC this morning. Not very dirty, nothing compared to @Chris pictured IAC. Cleaned it and the housing for good measure. No improvement.

Hooked up the bluetooth OBD reader using OBD Fusion on the iPhone and got no codes, but it did report pending codes of P0135 and P0155. I did some quick Google-fu and these codes *may* not be related. However I have not troubleshot this at non-operating temperatures and found that my Jeep will stall in short order when idling after startup.

So, what parts do I start throwing at this thing? New IAC? I figure new O2 sensors are just a good investment.
Yes, the IAC looks different on the earlier and later model TJs.

Those O2 sensors could very well be the cause for the idle issue. Fix those by replacing them with NGK / NTK sensors as mentioned in this thread: The Official Jeep Wrangler TJ Oxygen (O2) Sensor Thread

Then report back and let us know if that solved it.
 
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Echo5

Echo5

Member
Supporting Member
Aug 18, 2018
55
Eastern PA
Have you had the battery disconnected or has the battery gone dead recently prior to your idle problem?
I replaced the battery over a month ago (maybe two months now). Makes sense to check that the connections are secure. I'll report back on this tomorrow.
 
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Echo5

Echo5

Member
Supporting Member
Aug 18, 2018
55
Eastern PA
Yes, the IAC looks different on the earlier and later model TJs.

Those O2 sensors could very well be the cause for the idle issue. Fix those by replacing them with NGK / NTK sensors as mentioned in this thread: The Official Jeep Wrangler TJ Oxygen (O2) Sensor Thread

Then report back and let us know if that solved it.
I meant that the amount of gunk on the IAC was not near as dirty as yours pictured - apologies for that. I'm going to try checking the battery connections since I did recently replace it, thanks to insight from @Capt'n.

I will be replacing the O2 sensors in the near future even if the battery connection turns out to be the culprit. If the battery is not the source the O2s will be post haste.
 
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pagrey

TJ Enthusiast
Apr 10, 2018
506
Los Angeles, CA, USA
Both O2 sensors wont fail at the same time. I might replace the temperature sensor like @Steve Rodgers suggested. It can cause both codes. If one O2 sensor fails the code would likely be from just one bank.

Edit: the rough start might be the Jeep going "closed loop" or trying to use the 02 sensors when they are cold because the temp sensor is reading hot
 
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Jerry Bransford

TJ Guru
Supporting Member
Nov 9, 2015
10,641
Escondido California
Pull one of the spark plugs and tell us EXACTLY what brand and more importantly, what its model # is. You have a distributorless ignition system on your 2002 and it uses a waste-type ignition system which is very picky about what spark plug technology it will run well on. It'll miss and stumble with single-tipped platinum plugs like Autolite's AP-985 or Champion's 3034. It'll run fine on double-tipped platinum plugs like Autolite's APP-985, Champion's 7412, or Autolite's iridium-tipped XP-985.
 
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Echo5

Echo5

Member
Supporting Member
Aug 18, 2018
55
Eastern PA
Both O2 sensors wont fail at the same time. I might replace the temperature sensor like @Steve Rodgers suggested. It can cause both codes. If one O2 sensor fails the code would likely be from just one bank.

Edit: the rough start might be the Jeep going "closed loop" or trying to use the 02 sensors when they are cold because the temp sensor is reading hot
Apologies for the neophyte question, but which temp sensor am I replacing? Also, apologies to @Steve Rodgers for missing his post!
 
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Echo5

Echo5

Member
Supporting Member
Aug 18, 2018
55
Eastern PA
Pull one of the spark plugs and tell us EXACTLY what brand and more importantly, what its model # is. You have a distributorless ignition system on your 2002 and it uses a waste-type ignition system which is very picky about what spark plug technology it will run well on. It'll miss and stumble with single-tipped platinum plugs like Autolite's AP-985 or Champion's 3034. It'll run fine on double-tipped platinum plugs like Autolite's APP-985, Champion's 7412, or Autolite's iridium-tipped XP-985.
Autolite Iridium XP985 - replaced July 2018 as per info from this forum.
 
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Jerry Bransford

TJ Guru
Supporting Member
Nov 9, 2015
10,641
Escondido California
Good info. Since your battery is good and you're not having to jump start your engine (bad batteries can cause an inability to idle), it really sounds like your IAC (idle air control) is clogged and not passing enough air into the engine at idle when you're not stepping on the gas pedal. The IAC is the engine's sole source of air when you're not stepping on the gas.

Clean it with an aerosol can of throttle body cleaner. We'll try the easy way first if you can keep the engine running while at idle rpms. Remove the air intake tube from the top of the throttle body and then start the engine. With the engine idling, don't rev the engine, spray the cleaner into the throttle body, aim it at the Idle Air Control Passage Inlet where the IAC pulls its air from. The engine will die since it is flooding the IAC since the IAC sucks air (and the cleaner) when the engine is idling. Give it a minute for the cleaner to start softening the black gunk that collects inside the IAC. Restart the engine, keep the engine at idle rpms, spray it again. Keep this cycle going until you've gone through at least 1/3 of the can of not half. If it's idling ok by now, spray the rest of the can into the TB while holding the rpms up to open the butterfly valve plate at the top of the throttle body.

If you can't keep the engine idling well enough to spray the cleaner into the engine at idle rpms, it's time to remove the IAC so it can be cleaned which requires a torx adapter. It's a T-25 or close. Be gentle with the IAC, don't push-pull or twist the IAC's plunger any more than you have to. The cleaner plus an old tooth brush works well to clean it. You also need to clean the orifice in the throttle body that the IAC's plunger fits into.

If it still won't idle properly with a clean IAC you probably have a bad TPS (throttle position sensor) which can also definitely wreak havoc with the engine idle.

TB & TPS Sensor Locations.jpg
 
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Capt'n

Member
Mar 17, 2019
96
Southern Oregon Coast
I replaced the battery over a month ago (maybe two months now). Makes sense to check that the connections are secure. I'll report back on this tomorrow.
Well, while working on my jeep i had the battery disconnected for almost a month. I was concerned that when i reconnected the battery the jeep might not start well (even though it always had). Soo.. i pumped the gas pedal a couple of times while turning the key. She started right up and seemed to run fine until i tried to idle her. She would run really rough, sputter and die. What the heck. She always ran fine before and i didnt even work on engine during her time down. So.. I disconnected the battery again, waited a few minutes, and then reconnected it. This time when starting her I gave her no gas. Just a straight turn of the key. She started right up as before but this time she purred like a kitten at idle. Im not a "mechanic", but disconnecting the battery resets some sort of sensor. How you start it up after reconnecting the battery "teaches" the sensors what normal is. Not sure if this is even remotely the cause of your sensor issue but its only a 5 min task to try and you may get lucky without having to dig deeper.
 

KCsTJ

TJ student
Supporting Member
It's asking for bank 1 and 2 oxygen sensors. Replace them as referred to in post #7.
I had both same codes on my 05 right after I bought it with 101k.
A dealer had it and fixed nothing, just waxed it real pretty and put something on the flares that easily comes off at a car wash.
He fixed very little.
He Just kept resetting the engine codes and driving it imho.
That's a common trick with dealers
 

KCsTJ

TJ student
Supporting Member
So you take your car to a mechanic and now you're the expert?

Easy to spend money when it's not yours.
Huh? I cant afford a mechanic. I figure out things myself.
Look up the codes yourself smart ass.

Do you normally respond with smart ass questions when folks are setting aside their time to help an ungrateful POS like you.

Figure it out yourself retard.
 

pagrey

TJ Enthusiast
Apr 10, 2018
506
Los Angeles, CA, USA
Huh? I cant afford a mechanic. I figure out things myself.
Look up the codes yourself smart ass.

Do you normally respond with smart ass questions when folks are setting aside their time to help an ungrateful POS like you.

Figure it out yourself retard.
Both codes suggest the temperature sensor and both codes indicate a different O2 sensor. Basic logic and the factory service manual say the temp sensor is more likely because it appears in both codes. Helps that it is also less expensive. Does that make sense?

I am not a fan of people jumping to conclusions and spending other peoples money. You didn't even explain why to change the O2 sensor, just quoted some other post. The code does not say change the sensor. If you just figure things out for yourself maybe you shouldn't be helping other people out. People come here for experience, not you figuring things out.