Strange Behavior from 1990 XJ
 

Group:

I have a 1990 Cherokee Laredo with the 4.0 six, auto transmission, 4X4,
and 158,000 miles. The Jeep is maintained very well and generally is in
good shape. Recently it has developed a new problem. If I am cruising
(at 45 MPH for example) down the road with enough accelerator pedal
pressure to maintain my desired speed, all is fine. As soon as I lessen
the accelerator pressure (just to slow down a couple of MPH), my engine
RPM instantly drops way more than normal. I would guess somewhere
between 500 - 750 RPM. When this first started happening, I thought the
engine was going to die. After the sudden RPM drop, the
engine/transmission operates normally. It doesn't matter if I decide to
accelerate, slow down more, or come to a complete stop. There are no
other symptoms that I can find that may help solve this problem. The
vehicle works very well otherwise. Any suggestions? Thanks in advance.

Derek B.

Re: Strange Behavior from 1990 XJ
 

Derek Brown wrote:
> Group:
>
> I have a 1990 Cherokee Laredo with the 4.0 six, auto transmission, 4X4,
> and 158,000 miles. The Jeep is maintained very well and generally is in
> good shape. Recently it has developed a new problem. If I am cruising
> (at 45 MPH for example) down the road with enough accelerator pedal
> pressure to maintain my desired speed, all is fine. As soon as I lessen
> the accelerator pressure (just to slow down a couple of MPH), my engine
> RPM instantly drops way more than normal. I would guess somewhere
> between 500 - 750 RPM. When this first started happening, I thought the
> engine was going to die. After the sudden RPM drop, the
> engine/transmission operates normally. It doesn't matter if I decide to
> accelerate, slow down more, or come to a complete stop. There are no
> other symptoms that I can find that may help solve this problem. The
> vehicle works very well otherwise. Any suggestions? Thanks in advance.

Start with cleaning the connectors on the sensors. TPS, Idle Air, and MAP
sensors. And clean the idle air passage on your TB

The diagnostics chart on my site might help, but I'm unfamiliar with
this problem.


--
-- DougW -- 93 ZJ 4.0 http://members.cox.net/wilsond
HESCO Supercharger - 300W IASCA Stereo - Edelbrock IAS Shocks
Gibson Exhaust - rear DCpower - custom gauge install - Stillen Rotors

Re: Strange Behavior from 1990 XJ
 

Doug,

Thanks for the suggestions, I will give them a try.

Derek B.

Re: Strange Behavior from 1990 XJ
 

also check your EGR valve and related components.
Mine had some debris or carbon in that EGR transducer.
later,
dave

Re: Strange Behavior from 1990 XJ
 

Sounds like the early stages of throttle position sensor failure. (I'm on my
third one)

Doug
'92 XJ 163,000


"Derek Brown" <DEREKB0529@webtv.net> wrote in message
news:28192-3F1DB2A5-113@storefull-2296.public.lawson.webtv.net...
> Group:
>
> I have a 1990 Cherokee Laredo with the 4.0 six, auto transmission, 4X4,
> and 158,000 miles. The Jeep is maintained very well and generally is in
> good shape. Recently it has developed a new problem. If I am cruising
> (at 45 MPH for example) down the road with enough accelerator pedal
> pressure to maintain my desired speed, all is fine. As soon as I lessen
> the accelerator pressure (just to slow down a couple of MPH), my engine
> RPM instantly drops way more than normal. I would guess somewhere
> between 500 - 750 RPM. When this first started happening, I thought the
> engine was going to die. After the sudden RPM drop, the
> engine/transmission operates normally. It doesn't matter if I decide to
> accelerate, slow down more, or come to a complete stop. There are no
> other symptoms that I can find that may help solve this problem. The
> vehicle works very well otherwise. Any suggestions? Thanks in advance.
>
> Derek B.
>