still occasional rough idle and OK gas mileage

hey guys, i am still gettin that occasional rough idle but im still just gettin only like 9-10 miles per gallon, heres whats new, i know some of it has nothing to do with it but just listin what ive done, lookin for more ideas

1.starter

2.alternator

3.battery

4.water pump

5.timing chain

6.thermostat

7.cap and rotor

8.plugs and wires

9.fuel filter

10.air filter

11.oil change

whats your timing set at? and what about the emissions equipment. what shape is it in? mostly the egr. this will ***** with your idle and cause poor mileage. also leaky fuel injectors(or the orings).

Unfortunately, rough idle can be caused by a number of things. One possibility is a TPS that is starting to stick. Is your check engine light coming on? If so, pull the codes.

Good luck,

>-

is there any hesatation or miss fire?

there is no check engine light, the air tube to the cat is off, havent had a chance to fix that yet, it came off and the clamp is rusted on so i cant get it to stay on until i drop the exaust, i was also wonderin if the cat startin to clog has somethin to do with the mileage, the camaro i built actually at one point wouldt run cause the cat clogged, changed the cat and it was back to perfect. dont know what my timing is currently at, the s only a "slight" hesitation off of idle if it is below 700-750

88BroncoBlack said:

there is no check engine light, the air tube to the cat is off, havent had a chance to fix that yet, it came off and the clamp is rusted on so i cant get it to stay on until i drop the exaust, i was also wonderin if the cat startin to clog has somethin to do with the mileage, the camaro i built actually at one point wouldt run cause the cat clogged, changed the cat and it was back to perfect. dont know what my timing is currently at, the s only a "slight" hesitation off of idle if it is below 700-750

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A very definite possibility, if it is clogged you will have excessive back pressure. The cat being clogged should also exhibit itself in the power, making the truck kinda gutless.

>-

Even if your Check engine light is NOT on, check for codes.

I found a great article on how to test for codes.

http://www.fordfuelinjection.com/files/self_test.pdf

This will be of particular interest to those with 1984 through 1988 models, but is also excellent for those up to the 1995 models.

With an '88 the only tools you will need to check for codes is a short jumper wire, and a cheap volt meter.

Here are the connectors that you will find by the driver's wheel well, that you will jump with the jumper.

Alright guys idle problems = AIR BYPASS VALVE. Its $60 bucks and they commonly die slowing (a slow painful "rough" idle death) at 20 yrs old. Just save the headache and start your IDLE chasing here and the TSP at the same time. If that doesn't fix it, also coupled with a common tune-up then you have vacuum problems and worse (ie. worn valves, rods, timing gears....). A good clue is the fact that the truck runs fine and strong with throttle but "idles" crappy. This is because the Bypass valve or IAC only has to work when the throttle body butterflies are closed (meaning you are "NOT" giving it gas). Once you push the throttle its jobs it done until you let off the gas, then it takes over and keeps the truck running. If you pull the plug off while the truck is running it "will" stall immediately or atleast should because something you get a knuckle head that messes with the thottle body stop ***** that is set at the factory and should "never" be touched. They extend the ***** so it holds the thottle open slightly and thus you can change the RPMs as if you were holding the thottle. Really you are just doing what the IAC is suppose to do Only if screws up you truck cause it keeps wanting to lower the idle. You could even casue it the computer to swith to "limp" mode and then you shoot your gas mileage all to ****. Also keep in mind you Oxygen sensor tells your truck how it should mix the air and fuel. When you computer does get reading form it or gets readings that are not "normal" then its automatically runs "rich" in an effort to protect your pistons and valves from being burnt from a mixure thats too lean. Thus again... Bad gas mileage. Good Luck... and remember you could of bought four banger...

Big_Ford_POS said:

Alright guys idle problems = AIR BYPASS VALVE.

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NOT ALWAYS!

Give a man a fish and he eats for a day; teach him to fish, and he eats for a life time! IMO it is better to teach a man to fish than to give him one.

I agree.. IAC, TPS, vacuum leaks, plugs wires rotor and cap, are the most likely causes of a bad idle. Yet, mine was caused by a bad MAP sensor. Many drive 20 year old trucks and are too broke to fix them.

Some can afford to throw parts at a problem. Eventually they will get the right one... maybe. Others will trouble shoot and be more cost effective. Some prefer to troubleshoot because they know how!

The readers of this thread can choose whichever approach suits their needs and/or personalities, neither one is necessarily more correct than the other.

OK guys heres a new problem, i got up and dorve my truck today, idles at 2000 in neutral and 1400 in gear, every once in awhile it will drop back to the normal 800 or so, does this help narrow my issue

88BroncoBlack said:

OK guys heres a new problem, i got up and dorve my truck today, idles at 2000 in neutral and 1400 in gear, every once in awhile it will drop back to the normal 800 or so, does this help narrow my issue

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Yep.. it narrows it down to IAC, vacuum leaks, TPS (probably not, but still maybe) timing, and anything that affects timing in a computer controlled engine.

Why have you not pulled codes?

i think i did the codes correctly, what i saw is a 3-3 with the engine off and a 7-7 with it on, where do i look up what codes mean

ok redid it and got 33 and 73, egr valve not opening and "insufficient TPS change during dynamic check will these have to do with my idle and gas mileage, and which has to do with what

88BroncoBlack said:

ok redid it and got 33 and 73, egr valve not opening and "insufficient TPS change during dynamic check will these have to do with my idle and gas mileage, and which has to do with what

Click to expand...

EXCELLENT!!!

The TPS probalby has more to do with your idle, and to a certain extent your gas milage. The computer relies upon info from your Throttle Position Sensor (TPS) to set ignition timing, probably fuel injection, and certainly shift points of your transmission.

Gas milage may be adversly affected by the EGR, I am not sure if it would affect the idle. I am not a professional mechanic.

You may obtain additional information on each of these at

http://www.fordfuelinjection.com

Often the problem with the EGR is that it gets clogged with built up carbon, and it can be cleaned, and then reused. Not too long ago, my transmission was not shifting properly. It ended up being my TPS. I got a good amount of help from my friends here in a thread I started called something like "how to change shift points in a E4OD transmission" within that thread there is a link to a pictorial of how to change out the TPS, and my synopsis of how to adjust the TPS after installing it.

I am sure that you will find that thread very helpful.

I'll look for it to post it here.

http://broncozone.com/forums/index.php?s=&...ost&p=70938

Edit:... although there is a LOT of information in the above link, THIS ONE is instructional for HOW To Replace and adjust a TPS.

http://broncozone.com/forums/index.php?s=&...ost&p=72071

I'm proud of you. Many, if not most, just want the answer handed to them. Reading through that article is a little challenging, but you succeeded!

Let me know how else I can help.

Let us know how you make out.

Good luck

joe

ok guys fixed the rough idle, think it was a clogged cat, put long tubes with duals and its fine now, still have AVERAGE gas mileage at best though, and now the i have my exhaust leak gone and stuff i hear an occasional hissing from the floor behind the firewall above the trans, mostly when there is no load on the motor or at low speed, is the the AIR pump hose since its not hooked to the exhaust anymore and also if i sit in gear at a stop for a minute, there is a slight chatter underneath, so heres the deal i need some suggestions with what ive changed,

1. what could still be affectin my gas mileage

2. what is the on and off hissing im hearin, (its not the trans vaccuum lines, just came from the trans shop, all vaccum lines and modulator were changed, thats why i wasnt shiftin gears)

3. what is the chatter im hearin in gear at a stop