Only Six Miles Per Gallon!?

[ferrarifreakout]

I have a 1994 LS400 and I'm pretty sure I need to replace the idle air control valve because it smokes on startup. I used to get about 12 mpg on regular gas (rarely ever used) and almost 17 on premium 91 octane. I just did a muffler delete and now the smoke is more pronounced and mpg have quickly dropped to 9 and just recently, 6. Any help?

[IS400]

Do a search on here of how to pull codes on the engine. You jump a wire across some terminals in the engine bay and then turn the key on and count the flashes on the dash to get the codes if I remember. My guess is you have O2 sensor problems and maybe the typical power steering valve failure these cars get which draws power steering fluid into the engine and it burns while out the exhaust.

Why did you remove the mufflers? Did you take out the cats too?

[leximus]

I agree with IS400....but the terminal to diagnose your issue can also be found under the dash near your hood release (near your left knee). Here's a link to how to code read from this terminal using a simple wire: http://www.lexls.com/tutorials/intro/codereading.html

[leximus]

I agree with IS400....but the terminal to diagnose your issue can also be found under the dash near your hood release (near your left knee). Here's a link to how to code read from this terminal using a simple wire: http://www.lexls.com/tutorials/intro/codereading.html

[killerFatty]

I was getting 8-10MPG, but I replace the coolent temp. sensor and it got much better. I also have smoke on start up, but it hasn't bothered me enough to do anything about it yet. I also agree with IS400. Check the codes before you do anything else.

[ferrarifreakout]

Ok so I tried the diagnostic port on the driver's side with a piece of wire, but couldn't get the wire to stay in place... Then I tried to use the connectors in the engine bay, but for the life of me could not get the cap off to actually get to the connectors. I will back to you on codes and whatnot when I find a suitable paperclip or a way to open the cap.

[93ls400walt]

On the engine port pull up on the lip on the windshield side of the cap.

[eatingupblacktop]

Couple of questions: Does your cel light up/does it work? What condition is your air filter in? Are your tires prop inflated? Are any of your brakes dragging incl pk brk? In colder weather the pk brk cable can get stiff and fail to completely release. If all of these check out, then you have to determine whether it's fuel, air or ignition related. Worn/failing ignition parts, off ign timing, rich fuel mix, fouled sensors, all can contribute to poor economy.

[ferrarifreakout]

I know to pull on the lip of the cap haha, but thank you. The cap just wouldn't open. I have only ever had one CEL and it went away the same day. I haven't been able to take another crack at getting something to stick on the diagnostic ports because I had to study for SAT Subject Tests, but now that they are done I will take another look. Tires are properly inflated by the way. I never use my parking brake, so yeah it must be related to ignition or fouled sensors. Would ignition components to replace include wires or no? I know caps and rotors are a biggie.

[ferrarifreakout]

I just went outside and the engine codes are 25 and 26. This is a lean and rich air-fuel ratio malfunction respectively.

[ferrarifreakout]

Any ideas guys?

[VRicherson]

You can have the dealer inspect the entire car for less than $100. Just ask them the check it out. They will be sure to give you a list of everything that even remotely needs to be done to the car. I did this when I bought the car and asked specifically for a car purchase inspection. They charged 1 hr of labor to do it, which here in Montgomery AL was $78. Tell them you are buying the car, or that you are going to sell it to a friend and want to have a good idea of the condition, and ask them to inspect it. It wouldn't hurt to tell them that you are having problems in a specific area such as this.