Have a feeling my throttle body may be using me issues. Overall car runs pretty well, 2001 XJR. Today, at about 70mph, engine puttered briefly, also, I've noticed that for a couple weeks, gas mileage was lower than expected. I typically average 22-23mph city/hwy (mostly hwy), currently, am getting appx. 17-19. I had cleaned the throttle body in the past, and symptoms were similar, lower fuel economy, a little more sluggish performance. Car was sitting for appx. 10 months, so maybe it needs to be cleaned again? After the putter today, it did it again, then the "Christmas Tree" pattern on the dash, ASC, Trac Control, Engine Failsafe. Pulled over, turned off a couple minutes, then back on, issue seems to have gone away. Also, while driving in cruise control, seems better also. Not sure why, possibly something with a sensor for the gas pedal? Position sensor perhaps? It seems that at times, especially after aggressively accelerating (4500-5000 rpm) it does it, then when i let off gas it drops back down (as it ought to), then on it's own spikes up (about 2500-2800) than drops down to idle rpm (sub-1000) and throttle is limp/non-resonsive. Turn car off, turn back on, issue disappears. Btw, I've had it checked, no codes were present, so is tough to track down. Wondering if airflow may be cause o this behavior also? Planning on cleaning throttle body, MAFS sensor, breather tubes. Any other suggestions would be greatly appreciated.

Also, the air filter (believe it is stock, appears to be a K&H style. I understand there's a "special" method to clean the K&H modes, is that the same for the XJR, do they come "stock" with such a filter? It DOES look a bit dirty, how would I clean it? Am planning on taking car for a fairly long trip, about 1,500 miles each way, so would like to resolve this issue beforehand if possible. Once again, thank you all for any thoughts/suggestions.

 

A K&N air filter is not stock and if over oiled can cause problems with your MAF. Put in a paper filter and spray the MAF with MAF cleaner to rule out that issue but that would not cause the messages your are getting.


It sounds more like a throttle body issue and you don't want to leave on a 3000 mile round trip until you resolve it

 

the man speaks the truth. I had a K&N filter in my 911 an it destroyed my MAF. Go back to "stock" and see what happens...I bet it improves things

 

+1 KN filters will frequently mess up the MAF sensor. Your plans sounds right: clean MAF, change to a regular air filter, clean the throttle bore and plate (gently, carefully), make sure all is air tight.

Run a can of GUMOUT's equivalent to SEAFOAM (or SEAFOAM) through a tank.

Has the fuel filter been changed, might need a new one.

Assuming you have done the obvious: changed secondary tensioners!