Couldn't install the temp sensor - requires a deep socket.

However, after thinking about this, I think I may be working on the wrong end of the engine! The way the car starts and idles rough.. smooths out mostly (but not completely) once hot.. chug chug chug at the exhaust pipe.. I'm starting to think catalytic converter.

 

Actually clogged EGR ports will not cause a rough idle. An EGR that is stuck open will cause a rough idle. This is because the EGR only opens when your at cruise speed. It opens and dumps exhaust gases into the intake to be re-burned. Clogged intake passages will keep even a stuck open EGR valve from causing a poor idle. It will however set a check engine light for insufficient EGR flow. You might try a bottle of Techron in the gas tank. It works great for cleaning carbon off of the valves/pistons. It will not clean the intake though so you did not really waste your time there.

 

Fuel. Air. Spark.

Looks like you're covering the air intake part of it but others have also mentioned checking things such as fuel pressure. I would imagine the injectors are also old and possibly dirty.

I've had a low (not necessarily rough) idle in my protege since I bought the thing and I've come to realize that it can be very tricky trying to diagnose as a DIY'er. At least you've ruled out one of the more common causes (EGR)

It sounds like the car runs fine after warm up. I would imagine it's getting you from A to B. Is it something you can live with? The car is nearly 20 years old and it seems like all of those parts could add up quick.

Don't get me wrong, just trying to offer a different perspective. I personally enjoy working on my car and troubleshooting, but I do not have unlimited time and resources ($$$) either. Especially if the thing starts each morning and gets me to work.

 

An update.. I took it 2 different shops to get an analysis done. Both shops came back with the same thing - low compression caused by a blown head gasket and maybe some valve problems.

I have the shop manual on-hand, so I am taking the engine apart and will do the work myself. But, I have a question for the forum..

I have the timing belt off and it looks very good. Also, the water pump (outside) looks nearly new. I don't know if these things were changed recently by the previous owner or not. So, what should I do with these? Replace them anyway, or not? Maybe just put on a new belt and leave everything else as-is? Car just turned 115000 miles. What do you think?

 

Replace them for the peace of mind.

 

That sounds like good advice.

Now the $6,000,000 question.. how can I determine why it happened so it doesn't happen again?

 

You can only guess, not determine.
There are two likely scenarios:
The coolant may not have been changed and lost its ability to prevent corrosion. It could have attacked the head gasket.
The coolant was loo low and that caused local overheating and the expansion / contraction cycle weakened the head gasket.

Keep checking on your coolant now and then. Actually, the first few days you should check every time you drive. If everything stays o.k. you can check less frequently, like every week , then every month.

 

Well, I got the head off OK and am cleaning it up, but I'm wondering if it is usable. Please see attached pic. There is some corrosion around the edges of a few of the coolant passages. What do you think? Can I reuse this head as-is?

 

I don't think i would use that head.

 

Should I have a machine shop resurface it? What's the typical cost to have that done?