fast idle getting wrse 1995 Sport

[TGFH]

I have a 1995 Sport, Manual Trans, 4.0, replaced the IAC, TPS last year to solve the same problem. She's been running like a dream since. Last week idle went up to 900 to 1000, So being the good owner I am (lol) I cleaned the IAC, and checked for leaks. Idle went up to 1100 to 1200. O-K. So I replaced the MAP and the O2 since I have been meaning to do that - and for good measure I replaced the temp sensor and one-way valve on the Vac assist and even put clamps on the ends of the rubber hose - JUST TO MAKE SURE THERE WERE NO LEAKS! The idle is now 1500. It starts out in the morning cold at 900 to 1000 and as soon as I drive a mile and stop at a light - up it goes to 1500+. I don't have any check lights on and I don't have a code scanner. (yet)

Any ideas?

 

[TGFH]

No advise - Hmmm. With all the fast idle problems jeeps have I would think someone would have an idea - The more new items the higher it goes.

BTW did you know you can access the codes without a scanner? I found nothing there though so it has to be mechanical - I'll figure it out - always do.
Cheers

 

[Ecomike]

It starts out in the morning cold at 900 to 1000 and as soon as I drive a mile and stop at a light - up it goes to 1500+.

Sounds like my problem. The brake booster (vacuum booster) has a bad diaphragm that leaks only when the brakes are applied. It will get worse, and leak all the time eventually.

 

[Blaine B.]

So I guess a good test for that would be to unplug the vacuum line running to the booster and hold his finger over the end to see if the idle goes down?

Of course the motor will bog down a bit but I suppose its a good test anyway.

 

[Ecomike]

So I guess a good test for that would be to unplug the vacuum line running to the booster and hold his finger over the end to see if the idle goes down?

Of course the motor will bog down a bit but I suppose its a good test anyway.

Why would the motor bog down?

He should pull and plug the brake vacuum line, then apply the brakes with engine hot.

If their is a TPS ground problem the brake light power dump to ground could also feed back into the TPS ground and cause a high idle, but that is more likely with Renix than HOs.

 

[birchlakeXJ]

I would guess that you have a vacuum leak "somewhere". The high idle is the primary symptom of that. Now just to find the darn thing! Be sure to carefully inspect all vacuum hoses as a possibility; especially on the ends where they connect. Over time, these hoses deterioriate and can start to tleak. Spray a light mist of water or carb spray carefully around hoses and components; when the idle quality/speed changes, focus on that area. Good Luck!

 

[TGFH]

thanks for the ideas - I have checked the hoses - and even clamps on the vac assist for the brakes. The idle doesn't go down with the vac hose plugged. But it does drop a little with the CCV hose plugged. I think what I have here is a lot of leaks and I think at this point I will start replacing all the hoses. I did change the valve cover gasket last week but it was alreaduy idling a little high, FYI - I also put the old MAP back on and the idle is now about 1100 - better than 1500+. The check codes are all good except my coolant fan relay. AND I'm getting about 18 in city driving so can't be too bad. I have to think it's a leak.
Thanks again

 

[scottmcneal]

Have you checked the vacuum lines under the battery tray?

 

[Ecomike]

Does it increase when you apply the brakes?

Intake manifold bolts can be loose too.

 

[RichP]

Just went through this with my sons TJ and his buddy's YJ. Both had leaks in the intake manifold's, my sons was missing the last top bolt and spring washer and his buddy had one that was finger tight. Replaced the bolt and spring washer on his, idle dropped right down, retorqued his friends and same result somewhat, he replaced the intake/exhaust gasket and that fixed it. Those bolts and spring washers were pricey too.

 

[Ecomike]

Just went through this with my sons TJ and his buddy's YJ. Both had leaks in the intake manifold's, my sons was missing the last top bolt and spring washer and his buddy had one that was finger tight. Replaced the bolt and spring washer on his, idle dropped right down, retorqued his friends and same result somewhat, he replaced the intake/exhaust gasket and that fixed it. Those bolts and spring washers were pricey too.

Where did you get the spring washers, part number, contact?????

Please tell!

 

[RichP]

Where did you get the spring washers, part number, contact?????

Please tell!

Those were the one part I needed from the dealer, 1-33004255, made in USA, 3418-1-627 is whats on the bag. Pricey buggers...

 

[hanaxj87]

Sounds like your intake manifold bolts are loose.

Good Luck

Nick

 

[TGFH]

Problem solved - wasn't a leak after all. I did a bubble check - replaced several hoses and nothing changed - and all bolts were tight. Anyway I remembered something in the instructions when I replaced my IAC last spring. The measurement from the mounting base and the end shouldn't be more than 1 1/4". So I took out the IAC - AGAIN - cleaned it throughly - AGAIN - and the measurement was close to 1 1/2" Hmmmmmm - so I opened my wallet and bought a new IAC - AGAIN - and this one was shorter - installed it - drove it and - ALAKAZAM! it idled down to 750 - PERFECT. So beware of cheap Oreilly parts and never think just cuz ya replaced it 7 months ago that it's still good.

Thanks again for all the info. BTW I never knew there were vac lines under the battery.