Diagnose My Bug!

[oceanjoe89]

Alright, kids. Specs:

2003 NBC 2.0
6 Speed Auto Trans
83,000 miles

It runs smoothly, but sometimes I have issues starting. It turns over and over and over, but won't start. If I give it a little gas it will roar into life, or if I stop turning it over, wait a second and then retry the start it usually will sputter into life. It runs smoothly once it starts. This issue is most pronounced on warmer days.

Once in a while it will sputter and misfire when we experience a change in temperatures (say goes from a couple of really cold days in a row to a mild day and visa versa).

I'm fairly positive that my thermostat is shot. I have the P2181 code (Performance Malfunction in Cooling System) and it takes the blue light a long time to go off from a cold start even on a mild-ish morning.

I got a P0420 Catalyst Efficiency Below Threshold Bank 1 code the other day after a start where it ran rough as described above, but I cleared that code and it hasn't come back. I'm attributing it to the rough running that day.

What ya'll think? Anything else you want to know?

I was thinking that either my cat is on the way to plugged or my fuel filter is clogged-ish. I can hear the fuel pump run when I open the driver's door, so I've sorta ruled that out, and it runs smoothly after it does start with the exception of the situation described above where it runs rough on a damp morning or days where the previous day was significantly different in temperature.

I've been getting poor fuel economy for a while now (23 mpg highway). I've attributed that to the faulty thermostat which should be getting replaced within the next two weeks.

Plugs and wires were changed one year ago along with the air filter. Oil changes are done routinely, new tires this year...

Only things I can think of are MAF, Cat, or Fuel Filter...

Anything else sticking out to you guys?

Sorry for being long winded, just didn't want to leave anything out!

Thanks in advance!

[Smileybug]

Have you replaced your coolant temperature sensor? The new ones are green topped. The old ones fail and can cause problems and throw codes. Cheap part-should be under $30 even at the dealer. I would try that first before a thermostat.

[oceanjoe89]

Durr. I knew I was forgetting something. Just replaced that a month or two ago. It did idle smoother after doing that, so I know the last one wasn't the greatest despite it being green topped like the new one.

[oceanjoe89]

BUMP:

Okay, so a little bit of an update.

I've had the thermostat replaced. No change on anything
Coil pack was replaced. P2181 disappeared after chaning this.
P0420 was still plauging me. Replaced CAT after running something over.

P0420 comes back from time to time, and my MPGs are still low.

Thoughts?

I'm going to clean the MAF next week. Anyone have any input on the post cat O2 sensor? Does it affect fuel economy, or is that the job of the pre cat O2 sensor? Since the CAT was just replaced, I am thinking the O2 sensor might be going bad since that P0420 comes back from time to time.

CEL is off, and has been for some time. Depending on when it is scanned, I might find the P0420 code.

[The Cheat]

i had this code on a neon today, i replaced the first o2 sensor (upstream if you will). this is the one BEFORE the cat.

it cleared it right out.

[oceanjoe89]

you replaced the UPSTREAM one... i figured that one would toss a different code...

hmm... might look into that. Was it difficult to do?

[The Cheat]

it's not rocket science, any good shop can have it out in under 10 minutes.

if you do tackle it, the o2 sensor wrench from ecs is your friend. yes, it's pricey, but it WORKS.

[alg]

The issue you describe can be caused by a leak in a vaccuum line.
Based on the size of the leak and the current temperature, its very likely that the car would behave erradically.

The list of maintenance you have done on your v-dub infers that a lot of vaccuum lines were moved, or disconnected in the process.

The most likely area where vaccuum lines can get baked and crack is the area between the battery and the engine block (in a U.S. 2.0litre)

[oceanjoe89]

I guess I left one thing out. After the coil pack was replaced, the running rough while cold or on a damp morning went away.

Now I'm just trying to straighten out the P0420 code and the crappy fuel economy. Other than that, the bug is running better than ever.

Just to give you an idea, I get around 250-270 miles a tank, mostly highway... when I do the math, I get about 23 mpg consistently. If I do a total highway trip, I MIGHT see 26 mpg.

[cep]

When you figure out what's causing your crappy fuel economy, please post it. We've got one that gets just about exactly the same mileage.

[oceanjoe89]

I'm gonna clean the MAF and see what happens... Have you tried that?

[Canadianbugin]

Originally Posted by Smileybug

Have you replaced your coolant temperature sensor? The new ones are green topped. The old ones fail and can cause problems and throw codes. Cheap part-should be under $30 even at the dealer. I would try that first before a thermostat.

I would try this first plus the thermostat....

[bugsy98nb]

trade it for a TOYOTA

[oceanjoe89]

Originally Posted by Canadianbugin

I would try this first plus the thermostat....

Thermostat has been replaced.
Temp Sensor has been replaced.
Plugs have been replaced.
Wires have been replaced.
Coil Pack has been replaced.
Cat has been replaced.

I feel like I'm heading toward a dead end, but something has got to be out of whack for me to get 23 mpg highway.

[oceanjoe89]

Originally Posted by bugsy98nb

trade it for a TOYOTA

LOL you are oh so helpful, Jay...

[Canadianbugin]

Originally Posted by oceanjoe89

Thermostat has been replaced.
Temp Sensor has been replaced.
Plugs have been replaced.
Wires have been replaced.
Coil Pack has been replaced.
Cat has been replaced.

I feel like I'm heading toward a dead end, but something has got to be out of whack for me to get 23 mpg highway.

O.K. a couple questions....1.Did you replace the CAT with an OEM type(meaning)OBD 2 compliant? 2. Have you checked all the vacuum lines...Especially the one from the intake to the FPR? (fuel pressure regulator)3.Have you done an adaptation thought VAG-COM?

[oceanjoe89]

cat is an aftermarket one with the proper O2 sensor bung.

when i clean the MAF on monday, i will look the vacuum lines over.. is there a good schematic of them here somewhere?

and unfortunately i do not have a vag-com... yet... maybe soon though?

[Canadianbugin]

Originally Posted by oceanjoe89

cat is an aftermarket one with the proper O2 sensor bung.

when i clean the MAF on monday, i will look the vacuum lines over.. is there a good schematic of them here somewhere?

and unfortunately i do not have a vag-com... yet... maybe soon though?

Check the list of Vag's in your area might get lucky..?? I have not found one yet.... Someone else might have though..?? Chime-in anyone... There are a number which i have replaced though. Intake manifold to fpr and also under the intake plenum (between the intake and the valve cover) Found these cracked from heat.... GL ...KP...

[oceanjoe89]

hmm... okay. i'll definitely have to scope them all out with my dad... I'm hoping that just cleaning the MAF will help with the fuel econ...

as for the P0420, it hasn't shown back up after well over a week, and my commute includes at least 15 minutes on the highway, so I know i'm doing full drive cycles.

[oceanjoe89]

Thanks for all the help and input, btw