99 Avalon runs like a truck

99 Avalon had check eng lite on. 117,000 mi on car. OBDII told me EGR position sensor bad. Ran it for a month or so till we could (afford to) get it in for service. Few days before I take it in wife says it started running rough. This formerly ultra smuthe 3L V6 now chugs like a 56 Chevy truck on its last legs. Run it to the Dealer (I know spank me harder) told them about EGR code & had them “Diagnose.” So we need new EGR, they recommend a fuel injector cleaning flush, OK fine R&R EGR, do the flush, $695 later they quote me another $510 to change plugs wires & do a compression test & tell me I have codes P0300, 303, 304, & 305. Engine misfires on associated cyls. I say you’re whacked - for $510 I can get a new fridge to go w/ those plugs.

OK I put in new (aftermarket, but they fit ok) wires, resistance check the old ones, see like 13k each, new ones are like 3k each, no big deal? I break out the OBDII reader - same codes, same problem exists. I pull the plugs & inspect, they were replaced 17000mi ago look great, I swap the 1,3,5 bank w/ the 2,4,6 plugs, get same problem & codes. I figure hey 3 & 4 run off the same coil, do I have a common coil problem? So I get a new one put it in, retest, seems a little less chuggy, I notice code p0304 is not popping up anymore, progress??? Old coil tests ok.

I ohm out each fuel injector coil - 14.5 ohms each, = not electrically bad? I listen to these bad boyz w/ screwdriver, I think they all click or clack the same. I need like major chiropractic work from listening to # 3! Out of frustration (or stupidity) I take the thing back to the dealer (yeah, yeah, I know, I’m a slow learner already) to get this thing in better condition.

They run the comp test & tell me #4 is "weak at 125 while others were around 150-140. Another $385 bucks and the vehicle is in no better condition. Dealer service tells me we have “burnt” valves & need a valve grind job they estimate $4000 in cost to do. I ask them really, what causes burnt valves like overnight? One day it ran well the next day it didn’t.

This car never even thought about getting hot, never went low on oil & has had steady diet of Max life 5W-30 for several years now. Now that I’ve permanently fired this dealer & banished them to outer darkness I still need to fix the stinkin’ thing. I’m heading for the fuel system next, pressure flow checks, filter R&R maybe R&R all 6 injectors? You top gunz of auto repair got any ideaz? No, I don’t think takin’ it for a long ride off a short pier is gonna get it.

Thanks much Larry

You need to look at the flow chart for the P0300.

Heres a couple of the possible causes according to the shop manual for my 02 Sonata.

"P0300 Random missfire detected:

Possible cause:

VACUUM leak in air intake system

Low or high fuel pressure."

A vacuum leak would cause a lean missfire to all cylinders

Low fuel pressure would do the same.