Rough Idle, Fuel related?

[BumpLover]

When starting her hot or cold, she starts rough, pressing the pedal does help with the problem.
When shes hot she idles really bad. (IAC valve tries to compensate but the revvs go down as soon as they rise). As of this problem she overheats if I drive her for longer than about 10 minutes and fuel economy is horrible to say the least.



Spark plugs have but a few months on then (NGK Iridium), air filter is also new.
Coils are the ones she came with.

I have tested all the valves and sensors by resistance and have also read their values on a live code reader. (EGR, IAC, CTS, IAT, MAF, TPS) (Hope I didn't miss anyone)
PCV is good too.

I first thought of dirty injectors, when almost empty filled her with almost 40 gallons of gasoline and 2 bottles of Redline's SI-1. I have spent about 15 gallons of fuel and the problem only seems to worsen.

Could it be somethign fuel related? Say dead injectors, dead fuel pressure regulator or God forbid, fuel pump? Those are all originals. But I don't have the necessary materials to diagnose fuel pressure. Hopefully over here I can diagnose what's the problem, can't really spend more than $200 at the moment.

 

[UNC017]

With the overheating thrown in there, it sure sounds like a blown head gasket to me. Put a compression gauge on there, and I bet you find a dead cylinder. Or two.

 

[GMBoy]

Originally Posted By: 440Magnum
With the overheating thrown in there, it sure sounds like a blown head gasket to me. Put a compression gauge on there, and I bet you find a dead cylinder. Or two.



I agree - the mention of overheating was the red flag.

 

[punisher]

Originally Posted By: 440Magnum
With the overheating thrown in there, it sure sounds like a blown head gasket to me. Put a compression gauge on there, and I bet you find a dead cylinder. Or two.



Yup. Without the overheating thrown in, then you look for a vac leak in that situation.

 

[mechtech2]

Head or gasket.
Plugged cat.
FP regulator with bad thermostat or fan.

 

[BumpLover]

This is great...
For a J20A engine...
Standart Compression = 199psi
Low Compression Limit = 170psi
Max Difference Between Cylinders = 14.2psi

My numbers were:
Cylinder #1 = 165psi
Cylinder #2 = 210psi
Cylinder #3 = 190psi
Cylinder #4 = 200psi

This pretty much says they are dead right?
I will have to get a bank loan

I plan to have this vehicle for at least 8 years.
What type of engine rebuild should I have and how much should I expect to pay for it? Thanks!

 

[mattd]

add oil (small amount) to the low cylinder(s) and watch for compression increase. If it does, then complete overhaul. If not, remove head and have it rebuilt.

 

[BumpLover]

So, I was going to do the test again but I noticed this.
I took the radiator cap out and there was an inch and a half of coolant nowhere to be seen.
(Reservoir is at the same level it was)

Should I do the test again and add some oil to the low cylinder or this pretty much says it all?

 

[mattd]

coolant loss with overheating and poor idle definitely points to headgasket. Might be worth a shot anyway to see if compression increases with a bit of oil. This will let you know the compression ring condition.

 

[BumpLover]

Followed mechanic's advice and turned her on, let her idle for 45 mins (not running, just on) and turned her off for a whole day.

Found a sexy milkshake on the oil cap.

She is of course, getting opened up, she's getting a Fel-Pro MLS headgasket and new timing chains. Would it be overkill to get a full engine rebuild? I plan to have her for the long haul.

P.S. of course engine and cover is getting checked and rectified if needed.