weird idle issue

Well some of you may know. I just picked up this 88 cherokee. I didnt pass smog here is CA (High NOX), so I changed almost everything. I'm still getting a weird idle issue. It sounds almost like a vacume leak,but I checked. It will fluctuate just enough to see the needle move a little, but you can hear the motor a little also.

I've changed.
Plugs
cap
rotor
CPS
checked all the vacume lines
changed the oil
changed the injectors.
changed the o2 sensor


I did notice a small exhaust leak up at the manifold, but not real bad. I'm not ready for the rear broken stud removal yet unless you think this is it.

I'm also waiting for the TPS to come in the mail. That's the last thing I'm going to do before I sell it or keep it.

Help.

No new plug wires?

Have you sprayed the intake system to look for vacuum leaks?

All the CCV hoses-are they in good shape and not clogged?

Originally Posted by Factory Service Manual
TESTING
EGR VALVE
Valve Opening Test
1) With engine at normal operating temperature and at idle,
rapidly open and close throttle. Open throttle sufficiently to obtain
at least 1500 RPM. Movement should be noticed in EGR diaphragm.
2) If diaphragm does not move, probable causes are: faulty
vacuum signal to EGR, defective EGR diaphragm or defective
backpressure sensor diaphragm (if equipped), or leaks in vacuum lines
or connections.
Valve Closing Test
1) With engine at normal operating temperature and at idle,
manually depress EGR valve diaphragm. RPM should immediately drop,
indicating that EGR valve is not leaking and had been properly cutting
off exhaust gas flow at idle.
2) If there is no change in RPM and engine is idling
properly, exhaust gases are not reaching combustion chamber. Check for
plugged passage between EGR valve and intake manifold.
3) If engine idles poorly and RPM is not greatly affected by
manually moving diaphragm up, EGR valve is not closing off exhaust gas
flow. Check for carbon between pintle, leaking EGR valve gasket or bad
EGR valve.

I'll defenatly do the EGR test thanks. I tested it a different way, but this one seams to be good. I did put the TPS on today and it seamed to work ok and at least bring the idle up a little. I pullled the throttle body off and cleaned that also. It still fluctuated just a little bit, but seems to be a little better at runnning temp, but less fluctuation. The only thing I havent replaced at this point is the plug wires and the EGR sensor.

The plug wires look new, but maybe they are not.

I have 100K miles on the jeep.

My jeep has the same problem... i have replaced and checked everything, and its still there. Its a Jeep thing, more specifically, its a renix jeep thing lol

Have you properly adjusted the TPS? Super important.

Its the original kind and it is adjusted I think. Do you have the procedures for this off hand. If not I can look them up.

I drove it today and does run great otherwise and has way way more take-off and power it seams with the new injectors. What a frigen difference.

Post by Matthew Currie: From http://www.naxja.org/forum/showthread.php?t=925824
Here is the TPS test & adjusting procedure for the 87-90XJ 4.0 paraphrased from a service bulletin:

Quote: Test is done with throttle closed, connectors connected, ignition on, engine off. Insert probes through back of connectors to make readings. Use a high impedance meter. Adjust TPS by loosening mounting screws and turning in mount.

For manual transmission connect + probe to terminal A, and - to B. Take a reading, which should be in vicinity of 5 volts but probably lower. Note the reading well. Now move the positive probe to terminal C. The reading should be 16% of the previous reading.

For Automatic transmission, use the square, 4-terminal plug. Connect positive probe to terminal A, and negative probe to terminal D. Note reading, which should be in vicinity of 5 volts. Now move positive probe to terminal B. This reading should be 82% of the first. If not at 82% adjust the TPS until 82% difference is achieved.
Example 5volts times .82 would equal 4.1volts.

If you haven’t checked and cleaned your grounds hear is info on that to. VERY Important to smooth running Renix
XJ Main Grounding Locations
By 5-90
Main grounds:
1) Battery to Chassis [will need to be added in] Should be one on the passengers side fender liner (If one is not there from battery ground to the fender liner or radiator support frame, add one in #4 wire is OK #6 wire is best)

2) Battery to Engine Block next to oil dipstick support is a stud with a nut, but can be replaced with 3/8"-16 x 3/4 or 1" Hex Head Bolt. Then use brass flat washers to take up the slack if needed.
Since that's an electrical connection, I'd suggest using brass or bronze bolt to replace it with. The Zinc plating on carbon steel is supposed to prevent the steel from rusting, but why not just use something that isn't supposed to rust in the first place?

Clean the ring lugs and check to see if the small wire ring lugs are soldered or just crimped, if they are crimped only, Clean & solder them.

Grounded at the Renix engine oil dipstick bracket: are the ICM-- Ignition Control Module Terminal "B" of Connector No. 1 ground wire along with the ECU--Engine Control Unitground wire and Oxygen (O2) sensor ground wire; Plus the battery negative main cable.
Those are absolutely CRITICAL grounds for the Renix engine management.
http://www.naxja.org/forum/showthread.php?t=1047637

3) Cylinder Head to Firewall.
Clean and replace with #4 wire is OK #6 wire is best. Clean the ring lugs, and clean contact patches on the chassis (you only need to go about the size of a regular postage stamp, max) down to bare metal. Apply corrosion inhibitor (find it in your hardware store's electrical section) on reassembly.
Yes, the braided cable between the firewall and the head is the firewall-to-head ground strap.

4) Auxiliary grounds:
A) Engine block near dipstick bracket
B) Should be one on the passengers side fender liner (If one is not there from battery ground to the fender liner or radiator support frame, add one in #4 OK #6 wire is best)
C) May be one or two under the dashboard. Check the driver's side kick panel (may need to remove liner panel,) and check near steering column screws. These would be the main grounds for your instruments and switches. Clean & service.
D) Since you don't report trouble with the rear lighting, you probably don't need to look at it - but it should be tied to a chassis pillar behind the driver's side cargo area liner. #4 is OK #6 wire is best clean & service.
E) While you are at the back of the Jeep look for one that is grounding the fuel pump, clean & service.

A Scotch-Brite pad or wheel or a wire wheel (I use brass wire wheels) works well for cleaning ring lugs and for stripping metal. If a ring lug is dirty or corroded beyond cleaning, replace it (typical hardware store stuff is tinned copper, and perfectly acceptable.) Replace dirty/corroded screws, with a preference for BRASS (machine threads) or CRES (tapping screws.)

I find it useful to use brass flat washers under the screw heads, since it will increase the contact area between the ring lug and the fastening point (you've cleaned the chassis contact patch under the ring lug, and you'll sandwich it between the washer/screw head on top and the chassis down below. Again, probably overkill and doesn't do much, but it makes me feel better if nothing else).

Joe Peters quote “You have got to have good grounds. Without good grounds your coffee will taste like crap and your electrical components will behave erratically”.

I was looking at those the other day and noticed that the grounds were real dirty. I'am going to add a ground kit to it tomorrow and clean all the connectors. I have #6 wire ground kit I got off ebay. I have about 5 ground straps that go with the kit. A little overkill, but I'm all over it .

Thanks.......

Be sure to check the ground wire at the TPS, on both sides of the TPS as well!!!!!

murfs66 said:

I was looking at those the other day and noticed that the grounds were real dirty. I'am going to add a ground kit to it tomorrow and clean all the connectors. I have #6 wire ground kit I got off ebay. I have about 5 ground straps that go with the kit. A little overkill, but I'm all over it .

Thanks.......

Click to expand...

Be sure to clean them as advised in the previous post. Don't just add some. These are super critical to a good running Renix.