Bad gas milage, cant seem to pinpoint problem

[pcprophet]

Well for the past 2-3 months I've noticed my gas mileage has dropped drastically from 525km on a 40l tank of gas to 350km on a 40l tank.

well from right now i have hard starting when running for about 20 mins or so and shut the engine off and try to start it after 5 mins. cranks for 3-4 sec then revs high then settles down. this i thought a leaky FPR which was leaking, replaced and didn't solve the problem.

Replaced spark plugs/wires, coil pack's, 02 sensor, replaced with used EGR with 135,xxx on junkyard car, cleaned the passage from egr to tb clogged pretty bad.Fuel filter 6,000km ago,
Recent repairs
New water pump
4 New Tires
Front struts

Basically when i start the vehicle from cold start she will start up fine and idle good for about 10 secs then the rough idle starts by hearing the engine rev up and down almost like pulsating sound and shakes the car. once i rev up the engine there is no misfire and is running just fine but as i let off the gas she starts to idle rough. I've check for vacuum leaks but see nor hear any vacuum leaks. their isn't any carbon buildup on the exhaust and actually getting a lot of water leaking from the muffler like a constant drip. when i filled up the tank i ran some injector cleaner through the tank. I'm trying to get a hold of a fuel pressure gauge to see what pressure she holding and if at all my injectors are leaking excessive fuel through.
I've taken out the idle control needle and adjusted the needle to spec. might try to get replaced with used one also

i was also wondering if the fuel that was leaking from the fpr messed up the map sensor somehow and is causing it to sense to inject more fuel, gonna get a used one from junkyard and test it. I've checked the pcv valve and don't feel any blow by pressure.

recently did an oil change and noticed that she leaking some oil or maybe burning some oil. there are 3 spots of oil leaking that i can see and
1) is some sensor from under the power steering pump (maybe a crank shaft sensor?) seams hard to get at but their some fresh oil around the sensor? does the "unknown sensor" have an oil ring around it?
2) a lot of oil is dripping down onto the oil filter looks like from the knock sensor?
3) right under the passage way from the egr to the tb is a frost plug that has a build up of oil around it that needs to be fixed.

really don't know were else to look for or at. hate to keep adding parts that aren't fixing anything at all. maybe theirs something I've missed. hopefully I've explained enough to what kinda problems i'am facing

like always any help would be appreciated!! Thanks:D

[rixGAphx]

I'm suspicious of the IAC, and the 'needle cleaning' operation.
I've never handled an IAC, but I understand that the V6's IAC is touchy: Once the needle comes out too far, it will NEVER reseat properly (I've read that somewhere on here).

A fault with the IAC's control of the air would act just like a vacuum leak.

You might also get a spray can of winter starting fluid.
With the engine idling and running roughly, spray it under the hood at all the assorted vacuum devices, tubes, and connections.
When the fluid is sucked-in thru a leak, the rpm's rise and the idle smoothens.

Minor oil leaks are a nuisance, but they would not affect the engine's performance.
Unless the oil dribbles into an electrical connector: Oil is an excellent electrical insulator, and it can definitely affect the conductance of signals thru a connector.

Hope this helps,
-Rick

[HeyDace]

"525km on a 40l tank of gas to 350km on a 40l tank".

I don't know what that is in American. But a 13 year old car will have some problems. To me it sounds more like an injector problem which also could be causing your oil to leak out. Oil diluted by fuel will get past even good seals.

[pcprophet]

thats what i was thinking after i replaced my fpr and was still getting hard starts when warm/revs, i was lucky enough to get an oil analysis done for free and well get the results, hopefully its not bad. when i did the oil change i didn't smell any gas in the oil.

going to get a used iac and try to see if this helps.

this morning was a cold start to the day at around -7degrees celcius which i think is around 47 degree Fahrenheit she ran alot better with the cold air for about 1 minute until i opened the throttle abit and it rough idle came back :( thanks for the help, will update when i get some good result hopefully.

[poncho 1]

What's A Fpr

[pcprophet]

What's A Fpr

"Fuel Pressure Regulator"

[pcprophet]

well i was able to pick up a used iac from a lower mileage engine an got a hold of a tool thats test the function of the iac valve which allows me to move the motor up and down and tested ok. still have the idle problem. iam getting a CES light when im doing 90km/hr and decelerating. from what i thought was either a bad egr/02 sensors which i have replaced both and still having the light. lights goes away when i do around 120/130km/hr
hopefully this week i can get a hold of a scan tool, see whats it pulling up now. test my fuel pressure and get the egr checked out because iam wondering if one of the egr solenoids have gone.

when i was at the junk yard today i came across a 00 chev malibu with the 3100 engine and had lowmileage/had front end damage. anyway i got a hold of the fuel injectors but when i went to look at my fuel injectors they didn't look the same. are these injectors from the malibu compatible with the 94 3100?

This is what i picked up
http://69.0.158.19/live/W01331610704DEL.JPG

[ENGGUY]

Automatic transmission problems will affect the fuel milage as well. Also brakes dragging.
Can't always blame the engine. How about the air filter though more a problem in the old carburetor days.

[scotiez]

I get 23 to 24 mpg on the interstate with my cruise set at about 75 to 80 mph. I get about 17 mpg in town driving. It's been this way since its been brand new, I now have 17 thousand miles on my ga and i still get the same.

[mattcow]

I always get less than 550km's from about 40L and I do a lot of highway driving. If I set the cruise at 100 (usually its at 115 to 120) I could squeeze out close to 600kms.

[pcprophet]

well today i think i found the problem, i went back to the items that ive replaced, 02 sensors was working properly, coil packs were good, used map/iac that i tested from junkyard work fine, egr not so well. i unplugged the egr and the engine bogged down but the symptoms were similar to the rough idle. so i dismantled the egr valve to find the 2 out of the 3 solenoid were rusted and were moving so well. so took some memory cloth to the solenoid/passage to clean the rust out and reassembled. my rough idle were gone!!!! i only get a slight vibration when starting up cold but once warmed up she is running smoothly YAH!!!

Thanks for the feedback, i think the iac was also the problem. when i tested with an iac tester which also me to move the motor to move the valve up and down had a hard time moving almost sticking. used one from Malibu worked perfectly.