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Rpms dive when coming to a stop

4x4JeePmaNthINg

NAXJA Forum User
Location
Colorado
Rpms dive like its going to stall rifht before stopping, tgen back to normal just as fast. Its not consistent.
This has happened before and after cleaning the TB and Iac, new tps after.

I don't know if it's related but much more uncommon when starting it up and driving in the morning sometimes the 1st 100ft it lags on power.

?????
 
Is the TC unlocking?

What year is it?

What have you already done recently? Tune up....?
 
my bad, i was rushing typing on my phone at work.

99 xj 193000 Auto,

TB cleaned,
IAC cleaned,
TPS new,
plugs new,
wires new,
ignition coil soon to be new just cause i cant remember replacing it ever,
new plugs all .035 gap and it idles a tad higher and consistent 750 now, but nothing crazy above normal, it used to warm up and idle a hair under 750 with plugs that werent gaped properly.

no TB gasket, not sure i ever had one.

and these symptoms occurred before cleaning/anything new on the TB as well as remain after cleaning/ adding above new stuff.

life wise fuel pump is bosch newer, injectors BWD newer, cap&rotor pretty new, alt new, clockspring new, new battery ground cables.

it seems to do this the faster i slow down at stops. the quicker it slow the heavier the dive to 500-600 rpm. it never stalls but it seems like it wants to.

I plan to use a propane torch and use the gas to test vacuum leak, i read it should increase idle when passing a leak.
 
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Yea I've heard that about sensors, I haven't asked the stealership how much yet.

Does this sound like an Iac issue?
Should the TB have a gasket on a 99?
 
The IAC only kicks in if (1) vehicle is going less than ~40 mph (cant remember exactly, maybe somebody can look it up in the FSM) and (2) no pressure on pedal. You can test if its IAC related by going faster or by feathering the gas a little
 
The IAC only kicks in if (1) vehicle is going less than ~40 mph (cant remember exactly, maybe somebody can look it up in the FSM) and (2) no pressure on pedal. You can test if its IAC related by going faster or by feathering the gas a little

This only happens right before stopping so under 40 for sure.

I'm not sure what I'm looking for on your second recommendation by feathering the gas, is this supposed to produce the issue?

I tried tapping the breaks at multiple speeds and tons did rise, not sure if that's what we want to see for the TC.?
 
I tried tapping the breaks at multiple speeds and tons did rise??????, not sure if that's what we want to see for the TC.?

Tons????

I have had no issues for 12 years using after market Renix 87-90 jeep sensors on my 3 rigs.

I seriously doubt your problem is the IAC. When warm at idle, disconnect it, and drive test it. If the problem is still there, it is NOT the IAC!!!

Since you have no other problems it sounds to me like the TC is not unlocking soon enough. Could be brake switch, wiring, the #3 solenoid in the transmission valve body, sticky trans fluid (add a pint of trans-X. Run in neutral for 15 minutes, then drive it of about 15 minutes, drive it see if the problem stops). Could be the TCU, but the best suspect is brake switch, or connector, or varnish making the #3 valve stick.

O2 sensor maybe. Or TPS as well.

Is the brake booster leaking air?
 
My suggestion is give a little gas when you think its about to happen and see if it doesn't

This I could about guarantee would prevent it. But what does that mean?

Tons= Rpm apparently in my phones auto spell haha

Also by tapping the breaks and the rpm rising the TC is unlocking then right?

As for the break booster leaking air should this be something I could feel?
 
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Just for the hell of it, inspect the entire rubber hose that goes from the throttle body to the MAP sensor, and make sure it is 100% rot and leak free.
 
You'd hear it. When braking hard, a quick sound of air is normal(whoosh) as the pedal travels, but shouldn't be constant. If you constantly hear air escaping while holding the brake, it's leaking.

no air sound from the booster


mike ill closely check the MAP now just in case otherwise whats the next step fellas?
 
Have you pulled the spark plugs to see what they look like? Free test.
 
You skipped a step, an important step.

What did each and every plug look like????????????????????????????

Here are the guides they should have been compared too. You can drive it some, get 1-2 hours on it and pull them to see if they way too lean or rich, and which cyls have a problem...that leads to isolating the problem to less cyls, and 1 or 2 injectors, or injector wires, or....

https://www.google.com/search?q=spark+plug+color+chart+condition&tbm=isch&imgil=EhS9ps7_dyYXaM%253A%253BCMTj72K1f-j3dM%253Bhttps%25253A%25252F%25252Fwww.hdforums.com%25252Fforum%25252Ftouring-models%25252F1078036-reading-a-spark-plug.html&source=iu&pf=m&fir=EhS9ps7_dyYXaM%253A%252CCMTj72K1f-j3dM%252C_&usg=__iigw52gBb_zo****jiH1GFBVDng%3D&biw=1366&bih=609&ved=0ahUKEwie88nlwdzVAhXGeSYKHdXcCFQQyjcIQA&ei=aaCUWd6aIcbzmQHVuaOgBQ#imgrc=LThOcvB_Wn3ISM:

Have you changed the air filter?

plugs and wires are brand new now, with .035 gap, same symptoms before and after
 
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1) What does it do in park????? When you run it up to 2000 rpm and then let all the way off the gas?

2) What does it do in park????? When you run it up to 2000 rpm and then let all the way off the gas and hit the brake pedal?

If both are normal, if the rpm does not dive, then it must be TC Torque converter issue or #3 solenoid or varnish build up in the fluid.

If it dives in test 1 and 2, then it must be something in the engine controls, sensors....

Try this also:

3) Get it idling. Then disconnect the IAC power connector, then drive it (and rerun test 1 and 2) and see if the problem goes away. If it still dives, it is not the IAC!!!!
 
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