I recently bought my 99 xj sport and now it's having problems with the idle and. When in gear. Pressing the throttle cause's it to back fire and. Shake. I was told it could be the idle air solinoid but not sure. Any ideas???

 

Recently bought=not recently maintained... many people sell them without having done even the simplest stuff in a long time.

What have you done to it yet?

Clean some grounds. Clean your intake. Seafoam the gas tank. Do a tune up. Then look for the issue. . If it still exists.

 

I did a tune up. And also used. Some combustion chamber cleaner neither has. Helped any. I'm gonna try and clean the idle air solinoid tomorrow see if I get any results

 

I pulled the idle air solinoid and it's like brand new. Still trying to. Figure out the issue

 

1. Is the check engine light on or have you seen it on? If so, retrieve codes for clues and guidance on root cause.

2. FUEL PRESSURE. This must be verified early in the process for these symptoms. The fuel pressure spec. for the 1999 4.0 is 49 psi, plus or minus 5 psi. Must be verified with a fuel pressure gauge, which can be rented inexpensively from many parts stores; call around for availability. Verify fuel pressure before moving onto more complex possibilities; the throttle position sensor being on the short list.