Hey guys. I've been driving my 98 civic LX for a bit over a year now and it has 180k on the original engine. The previous owner wasn't great with the maintenance and it is starting to struggle a bit. Let me list my problems and see if you can come up with anything:

1) City mileage is "lacking" (I get around 22-25mpg city, and that is driving EXTREMELY gently, shifting around 2200rpm and cruising in 4th gear.)

2) Highway mileage is only okay (I get around 36mpg on my 50 mile commute, tires perfectly inflated, going 60mph with cruise control on).

3) Cruise control is spotty. It fights me. I'll cruise up to 60, hit cruise. The engine will lull for a second, then speed up to 65. If I'm lucky, it stays there. Sometimes cruise control decides that I'm going to go 85 and I have to fight it with my brake. When the engine is deciding that I'm going to go 85 despite me setting the cruise at 60, pressing down the clutch results in the engine redlining.

4) Idle is rough when engine is warmed up. It idles anywhere from 300-700 rpm when warm, around 1100rpm when cold. Another odd thing: the engine idles higher if I am not touching the brake pedal at all. Pumping the brakes messes with the idle and can push it up to 1700rpm temporarily.

5) There is a loud whistling noise occasionally (especially when engine is VERY cold and just starting or under fairly heavy acceleration).

6) Code 0420 (catalytic converter code) pops up every 50 to 200 miles.

Things I have already tried:
1) Full tune up (properly gapped plugs, new plug wires, fuel filter, oil change, seafoam and running v-power shell gas to clean up my injectors).

2) I tried to set the ignition timing, but I couldn't find the mark on my crank pulley. I'm fairly sure there isn't one. I hooked up my gun and tried to figure out how the timing is now, and no dice. Kinda weird.

Any help would be excellent. Thanks guys.

 

In regards to the timing mark, theres a groove in the crank pulley. It could be that because the engine is so crusty (assuming it is since it has 180k on it) there is grime filled up in the groove.

 

The marks on the crank some times disappear.
There should be 3 marks are in.


Does the car have a intake? Have you checked it for vacum leaks?

 

It's all BONE stock. But I'll try cleaning off the crank pulley when I open the hood next time with simple green and a scrubby brush.

And I had a vacuum leak when I bought the car between the IACV and the TB, but I got a new gasket and it's fixed. I made sure it was airtight with some TB cleaner sprayed all around the IACV/TB joint and the idle didn't fluctuate at all.

I'm thinking I'll probably rehose the engine (14 year old rubber!). All I need is some decent hose right? I'll go down to napa and pick up a box of the high strength vacuum hose. Anyone know what size(s) I'd need?

My best guess is the cruise control is vacuum controlled and the vac leak forces it to steal my gas pedal from me (when it goes up to 85). Is the CC vac controlled?