New here, first question about bad idle 96 4.0.

[Yellow Defender]

I am an old timer to the Defender as have an original 97 NAS. A few here know me from the D90 mailing list back in 98.
I purchased an old used 96 Disco with 140K as a play toy and had for 2 months. Dirt cheap, and put a fuel pump in runs like a champ.
Typical JEMS 4.0 with an auto However has a crazy high idle about 1500 when hot.
I swapped the MAF and TPS from other old 4.0 motors laying around past 30 years (used but give exact same results).
I have not pulled the plenum to clean or inspect because it worse when hot so doubt dirt. Also I look see if any vacuum lines loose on brake booster Etc not noticed.
On the highway no hesitation, sluggish and no backfire or smoke, just the idle is bad.
I have a $50 OBD dash gauge from eBay and it mostly run 186 degrees and long idle with AC on never over 206.

BTW any old Rover Mechanic around Houston / Sugar Land let’s talk as $ IPA beer.

Alan Dobbs
The old Gulf Coast Rovers

 

[robertf]

Welcome Alan.

I suspect you need to reset the adaptive values. The tps closed value gets stored as the all time minimum voltage measured. if you put a different tps in there or it wears and has a slightly higher voltage than what is stored as closed it thinks your on the pedal and it executes the IAC reset routine resulting in a high idle

You still got any wheels in the warehouse?

 

[kris812]

+1 on reset adpative values with Roberts tool on android. Also worth pulling the IAC and cleaning before that. They do get dirty and it's a very easy job..

If that doesn't fix it, then it's probably a vacuum leak. Somewhere..

 

[4Runner]

Check your vacuum line to your fuel pressure regulator. It’s back and out of the way. Pull the screws out of your TPS and leave it in place. Start the engine and very slowly move the TPS one way then the other to see if it gets happy. If that works then slot the TPS holes and lock it down or have the values reset. If it doesn’t then you know to keep looking elsewhere. Good luck.

 

[Yellow Defender]

Welcome Alan.

I suspect you need to reset the adaptive values. The tps closed value gets stored as the all time minimum voltage measured. if you put a different tps in there or it wears and has a slightly higher voltage than what is stored as closed it thinks your on the pedal and it executes the IAC reset routine resulting in a high idle

You still got any wheels in the warehouse?

Thanks and Yes have some old stock of the wheels. DM me

 

[boxster]

Clean the throttle valve opening and the MAF then reset the adaptive values, down load GEMS ECU APP for Land Rover to Android phone and buy a ELM 327 dongle should correct your idle problem.

 

[kris812]

Shotgun this problem in the face: Clean MAF, clean IAC, check vacuum lines, check TPS with ELM327, and reset adaptive values..

To note, I had a bad brake booster leaking vacuum and was a PITA to locate.

 

[robertf]

Shotgun this problem in the face: Clean MAF, clean IAC, check vacuum lines, check TPS with ELM327, and reset adaptive values..

To note, I had a bad brake booster leaking vacuum and was a PITA to locate.

what were the symptoms? mine has started hissing when I really get on it.

got a proline in the box but been too lazy to swap it

 

[StangGT5]

I had one do this because a previous owner adjusted the throttle or cruise control cable to hold the throttlebody open slightly. I twisted the adjustment collar and down the idle went. Just something else to check.

 

[kris812]

what were the symptoms? mine has started hissing when I really get on it.

got a proline in the box but been too lazy to swap it

At first I seen LTFT on both banks were crazy high.. And when WOT or flooring it, I would hear faint hissing inside the cabin. Also truck had Terrible brakes I wouldn't trust others to drive.. New boster from RN I think it was proline and now I can squal tires in a pain brake at 45mph on 32" tires, stock brakes except braided lines.

Also worth checking the O ring and seal between the master and booster. That leaks and it's like an intake leak. Backyard test is to wrap that area with wet towel and see if idle changes. Or squirt some Nector on it and see if Revs increase from the meth, but that'll toast that O-ring later.

 

[salvvia]

Try another MAF and check the crank pos sensor and cam shaft sens and wiring i have had that cause some weird stuff.
The crank pos sens wiring got cooked and was gave intermittent signals .

Welcome
And ride dirtay.

 

[robertf]

At first I seen LTFT on both banks were crazy high.. And when WOT or flooring it, I would hear faint hissing inside the cabin. Also truck had Terrible brakes I wouldn't trust others to drive.. New boster from RN I think it was proline and now I can squal tires in a pain brake at 45mph on 32" tires, stock brakes except braided lines.

Also worth checking the O ring and seal between the master and booster. That leaks and it's like an intake leak. Backyard test is to wrap that area with wet towel and see if idle changes. Or squirt some Nector on it and see if Revs increase from the meth, but that'll toast that O-ring later.

I replaced mine just now and almost went through the windshield at the first stop. i didnt realize how bad they were

 

[kris812]

I replaced mine just now and almost went through the windshield at the first stop. i didnt realize how bad they were

Haha You're not the only one that has changed boosters and sent everything flying forward!

I think the boosters start leaking so slowly we never noticed we were the frog in boiling water.