Well they're right. Process of elimination is really the only way to fix the problem. Fortunately/unfortunately your truck was built before there was a sensor for every single engine component. It makes working on newer cars a pain in the ass, but also allows the computer to scan all these sensors and locate the problem immediately. With your vehicle it's more of a hunt-n-peck process of elimination. You'll either have to do the hunting yourself or pay a mechanic lots of $$ in labor rates to do it for you. 1. The firing order for your engine is 1-5-3-6-2-4. Check the #1 cylinder spark plug. You should have plenty of room to get in there, pop the plug boot, remove the plug and see if the electrode is blackened. Total time investment will be <10 min max for you. If it's going back to the garage this week anyways just ask the mechanic to humor you and do this. Should take him all of 3 minutes. I think at this point the original problem (too much fuel) has caused other problems which is leading to the vehicle running worse and worse. (I'm still putting my money on a faulty IAC valve though)
That is my second guess, my first would be the coolant temp sensor. My cts just went on my 02 civic, and no codes were thrown. It has probably been gone for 2 years, and i thought it was just my lead footed driving habits that were causing my poor gas millage. Just for fun, i got it hooked up to a laptop to see what everything was doing, everything was fine, except that my engine temp was reading 0. For some reason it was not throwing a code.
If the sensor fails in a mode that still sends a valid temp signal, it won't throw a code. If it was reading zero, the computer sees that as inside the valid range. So, unfortunately, I would have the mechanic do this: Replace the IAC valve, replace the coolant temp sensor, check plugs, clean and reinstall or replace if necessary. Maybe replace O2 sensor if needed. You could start at the beginning, and do just one at a time, or do a few at a time, or all of them. Luckily, your engine is running rich and not lean. If it had been running lean, you'd be stuck with much, much bigger problems by now.
Runs fine (when it starts), no knocking. I don't know about running hot - nothing's coding or showing hot on the gauges. I think it's coding lean, meaning it's dumping too much fuel into the mix.
If it's dumping too much fuel into the mix, it will code as running rich. Coding lean means the O2 sensors are picking up un-used o2 downstream from the combustion chamber, meaning there is not enough fuel. That's a potentially really bad condition, because if the amount of fuel in the mix is too low, the mixture can ignite from the cylinder pressure before the spark plug fires, throwing the timing of everything out of whack, and potentially doing some internal damage. Lean mixtures also burn hotter, and can literally destroy your pistons, cylinders, and valves. It sounds to me like your truck is fluctuating between rich and lean. Running rich will give you bad mileage, but probably not throw any codes. Running lean will throw and store the codes. You really can tell a lot from looking at your spark plug tips, a good mechanic will be able to tell if it's running rich or running lean just by looking at the tip of the spark plugs. If it's alternating between the two, it might be harder to tell, but you'll be able to see that there's something wrong.
From Repair Pail with regards to codes P0171 & P0174: That's what I was trying to say, probably badly. Sorry for the confusion.
Ok, yeah that sounds right. I think I got confused because it's a little different from the way GM lean codes are thrown. It's been a while since I've dealt with those as well, so it was probably my fault. I keep coming back to the IAC valve, maybe even the PCV valve (I'm fairly sure your truck has one). Somehow more air is getting into the engine than is supposed to. Check any of the emissions crap as well, and check out any vacuum lines on the engine. I guess a vacuum leak may cause or at least contribute to your problems. It sucks because it's such a general symptom, it takes a lot to track it down.
Any time you get symptoms that are erratic and/or intermittent on a modern car, I almost always check for vacuum leaks first. Vacuum leaks are notorious for being hard to track down and causing strange things to happen. If you haven't already, visually inspect all of the vacuum lines and intake plumbing under the hood. You can also spray likely looking areas with some brake cleaner while the motor is running. If there's a leak engine speed will increase when you spray it with brake cleaner. You might also check your catalytic converter to make sure it isn't plugged as that can cause stalling and poor fuel economy. With what you've described, a problem with the cat seems like a long shot but it seems like you've checked most other stuff.
My girlfriend's father has a '98 F-150 and was having similar problems--in his case, the air/fuel ratio was off enough that it was shaking like a crack head. He brought it to a mechanic friend of his and the guy sprayed brake cleaner on a couple of the vacuum lines that normally suffer from dry rot or cracking. He hit one of them and the truck ran perfect for about 5-10 seconds and then went to shit again. The brake cleaner added enough "fuel" to the increased amount of air to even everything out, at least long enough to find the area that they should be looking in. About 5 minutes later, he found a very small hole in a little rubber elbow joint. When he covered it with his finger, everything ran fine. $11 later, and the elbow was replaced and the truck runs great.
Hey Dcc001, have y'all looked into the EGR [exhaust gas recirculation] valve (and related passageways) at all? An EGR valve that has a bunch of junk stuck in it and is staying open at the wrong times will make your car stall or run lean, because it is drawing burned gasses from the exhaust system. It sounds to me like either an IAC problem or an EGR problem when you have trouble idling on a fuel injected vehicle.
It was in the shop all day today. Here's the high points of what the mechanic says/thinks: - spark plugs are light in colour - did not act up or stall when they drove it (of course) - he strongly thinks the weak fuel pump in the front tank is the root cause of the problem. The more I think about it, the more the symptoms sound like a hot soak condition; which points at fuel pressure. My mechanic asked me to put about $20 of gas into each tank and drive it as much as possible in the heat and keep a record of when it does it. I was thinking it was acting up on either tank; however, I'm not sure. I'll drive it this weekend and - provided it's hot out - I'm confident I can get it to do the stall/shudder thing and see if it's doing it on just the one tank. Thanks for all the advice, everybody. It's going to be a good starting point if the fuel pump thing doesn't turn out to be the problem. At least the mechanic's aren't screwing me around; they aren't charging for all this diagnostic time, and they aren't pushing me to replace anything until they know for sure what's happening.
FYI, we've seen something similar, but it was a problem with the fuel pickup in the tank of our race car. Tank would expand when it was heat soaked, and would slightly shift the pickup location. In our case, it was into a bladder that had slightly shifted, but it was enough to really screw up performance. Might want to ensure that the pickup is clear, and there isn't any crap that might be causing a fuel pickup problem. It's a stretch, but stranger things have happened. $0.02
The worst part about being an automotive journalist is I can't free lapping on Mondays due to my 9-5 job. I'll live.
I am putting my money on the MAS (mass airflow sensor). Or much like Guy said, the IAC, the fact that it does it while moving, or slowing to a stop has me looking at these two sensors. The fact that its starting to happen as its warming up really has me looking towards the MAS. Usually as the density of air decreases in the summer time the engine has to compensate by adding more fuel to achieve the 14.7:1 ratio. I'm leaning a little more towards MAS than the IAC tho. Honestly, if you have over 100,000 miles on this truck you should replace both of them anyway, just cause. I know it isnt typically recommended, by why not? Might cost you a little over $200 but big deal. New parts to not go bad.
I'm moving up to Alaska in a couple of months. i wanted to know if anyone has any experience with Land Rover Defenders. I love my Scout, but it's staying here. I'm going to be looking for a used one (obviously). Are getting parts a complete pain in the ass? I'm not interested in collecting, this is going to be a work truck. I take care of my vehicles, but I'm not into polishing or having to have the prettiest car. This is going to be used for utility. i don't really want a truck, having to help fuckers move is not in the gameplan. I really like the body style of the Defender, so any gear-heads have opinions?
Defenders are pretty pricey for what they are. If you're going to be using it as a work truck I'd look at something else. Maybe a Tacoma or 4Runner, Jeep Wrangler? Or even an older Land Cruiser if you like the boxy classic body style. I'm not sure how many dealerships and distributors Land Rover has in AK but I know parts are hard to get in a timely manner around here. A buddy of mine has two of these, one is for show (D-110), one he takes off road (D-90) often. Extremely capable vehicle but honestly they're nothing special. I go everywhere he goes in my 3" lifted Jeep Rubicon. Also they don't tow well if that factors in at all.
Land Rovers are also not exactly known for their stellar reliability, as far as I know. I'd also throw in previous generation Nissan Pathfinders into the mix. They come with a low-range, manual tranny on some models, can tow a decent amount, and are pretty reliable. I had a 96 that I bought used with 110,000 km on the ODO. Ran it up to 245,000 km before trading it in for our Rogue and only had to replace wear-n-tear items. Used it as a winter beater up here in Canada. The 1996 to 2000 came with the 170 HP 3.3L V6 and are a bit lethargic, especially with the 4-speed auto, but reliable. In 2001 they introduced the 3.5L V6 VQ-series engine (similar to the engine used in the Maxima, 350Z, Altima, etc) which bumped HP up to 250 in the manual, 240 in the auto. Acceleration improves accordingly while maintaining similar fuel economy to the 3.3L, but the VQ35 requires premium fuel. XE and Chilkoots are base editions, SE's the 'tweener "sports edition", with the LE being the leather heated seats, sunroof, 6-disc indash, automatic climate control, top-of-the-line edition. Starting in 2001, the LE's (although SE's could be optionally equipped) came with a rotary switch to control the centre diff and had an "All-Mode 4WD" (basically AWD), and dedicated 4-Hi, 4-Lo and 2WD. Lesser models and models prior to 2000 have the part-time 4WD only with a separate shifter for 4-Hi, 4-Low and 2WD. Still, for ultimate off-roading capability nothing beats a Jeep.