Rough idle

[Blackgeetee]

Recently my car idles roughly just as the engine fires up. It almost seems like it idles too low initially (just under 1000rpm) right as it starts up, and it shakes a bit and sounds crappy. Then a few seconds later it's almost like the computer knows something's wrong and advances the timing because the engine starts idling around 1700rpm. Then after awhile it starts to lower back down towards 1000 and is much smoother. I have had a dyno tune recently so it should be running flawlessly. It runs great other than the first few seconds after startup. Any ideas guys?

Thanks!:beer: :beer:

 

[GR8WHITE]

It just is doing that to warm the motor up, that's all. It just more pronounced now after the swap. ;-)

 

[Blackgeetee]

Okay, thanks!:beer:

 

[hillie16]

Yeah what he said. Do you have a chip?

 

[Blackgeetee]

Originally posted by hillie16
Yeah what he said. Do you have a chip?

Yup, had that burned with the dyno tune. My air fuel mixture was tuned beautifully, the guy did a hell of a good job.

Since it runs great other than the first few seconds after start up I figured it was nothing, but thought I'd ask to make sure.

 

[hillie16]

Cool, whether it was custom burned or not was my next question.

 

[1BadAzzGT]

If it idles badly or "hunts" you can also check your clean/check/replace your IAC (Idle Air Controller). It will cause the car to idle funky as well.

 

[sohowcome]

Originally posted by Blackgeetee


Yup, had that burned with the dyno tune. My air fuel mixture was tuned beautifully, the guy did a hell of a good job.

Since it runs great other than the first few seconds after start up I figured it was nothing, but thought I'd ask to make sure.

I dont know if you have been around the grand marquis when it starts, but it will sputter then roar to life, takes a good minute for it to calm back down.

Don I have a seperate question, I was driving down the road the other day adn all the sudden my oil pressure dropped, to well under normal, it wasnt in the danger zone, but way lower than I have ever seen it, I stopped at the next service station, popped the hood looked for leaks, none, check the oil, full. I started her up, oil pressure still read low. I gave it a little prayer and off I went about a minute later it went back up and it has been fine since.

My question is this, do you think it could have been a quircky occurance, or is my oil sender or oil pump going out??
Thanks
-Zach

 

[GR8WHITE]

It may be the oil sending unit. The oil pump would have given some signs that it wasn't functioning properly. Temp would have been higher due to the lack of oil flow. Along with a few other things. I'd keep it simple to start with. Check and/or replace the OSU. It may just be the wire loose on the OSU connection.

 

[GR8WHITE]

Try this and see if it helps some Joel.

When youfirst put your key in the ignition, turn it to the on position, nto the start position. Listen for the fuel pump hum. Wait just a second or two, a pause to hear the hum, and start it then. Let me know if that helps any.

 

[Blackgeetee]

Originally posted by GR8WHITE
Try this and see if it helps some Joel.

When youfirst put your key in the ignition, turn it to the on position, nto the start position. Listen for the fuel pump hum. Wait just a second or two, a pause to hear the hum, and start it then. Let me know if that helps any.

Oh man I never thought of that, that's a great idea. I've seen other people do this (as a habit) but I never even thought of doing that. That could help. I'll definitely let you know, thanks!:beer:

 

[sohowcome]

Originally posted by GR8WHITE
It may be the oil sending unit. The oil pump would have given some signs that it wasn't functioning properly. Temp would have been higher due to the lack of oil flow. Along with a few other things. I'd keep it simple to start with. Check and/or replace the OSU. It may just be the wire loose on the OSU connection.

Don,

Thanks for the info

 

[Blackgeetee]

Originally posted by Blackgeetee


Oh man I never thought of that, that's a great idea. I've seen other people do this (as a habit) but I never even thought of doing that. That could help. I'll definitely let you know, thanks!:beer:

Well I tried it a few times but it didn't help. Still a little rough at first. It's almost like the engine thinks it's cold outside, weird. Anyway, thanks for the advice!:rolling:

 

[GR8WHITE]

When was the last time you changed the fuel filter? It sounds like it isn't quite getting enough fuel right away.

 

[Blackgeetee]

Originally posted by GR8WHITE
When was the last time you changed the fuel filter? It sounds like it isn't quite getting enough fuel right away.

Yeah I thought of that too but I replaced that right after I bought it with 38K miles. It now has 62K. I kind of wonder if my plugs are gapped right.

 

[sohowcome]

Originally posted by Blackgeetee


Yeah I thought of that too but I replaced that right after I bought it with 38K miles. It now has 62K. I kind of wonder if my plugs are gapped right.

might make sense with the head swap and all..........

 

[GR8WHITE]

I'm sure some of our more experienced 5.0 guys will help on this one some. If I remember right when the 5.0 guys change heads,cam, and intakes they sometimes had to drill an additional/enlarge the hole in the TB to allow enough air at idle. Also the TPS voltage has to be reset.

I'd change my fuel filter every year You never know what is in the tank until it clogs the lines. Plus it is a good maintenance step according to the owners manual.

The gap should still be .052, you might need new plugs maybe. The gap should still be the same.

 

[Blown306]

Originally posted by GR8WHITE
I'd change my fuel filter every year

Yes...I change my spark plugs every year as well, cheap parts to help insure a good running engine. Regarding drilling the TB, I know some guys have done it, but I wouldn't unless absolutely necessary. Typically with a head/cam change you'll run rich at idle, and it will hunt and surge. Mine was so bad the engine would die. Try the following procedure to get the IAC adjusted and don't forget to reset the TPS as mentioned above. If you still have bad idle problems, you'll probably need to increase the IDLE_AIRFLOW parameters in the EEC with a tuner or a chip to increase the IAC duty cycle. HTH, good luck...


Begin with a cold vehicle. The idea here is to get the car to a firm cold idle with enough airbleed capacity left in the idle circuit for IAC adjustment.

The idle stop should be set first. Back out the idle stop screw, away from the bell crank arm, until about 1/2 turn past the point where it no longer makes contact (blade fully closed). Using an 0.010" feeler guage, tighten until gauge just drags between screw and bell crank arm. Remove feeler gauge. Tighten screw exactly 1 1/2 turns. If the screw is very loose, put a drop of locktite or silicone on it, so it doesn't work out of adjustment.

Now remove the connector to the Idle Air Controller (IAC) just on the other side of the throttle body. Start the car and allow to warm for 2 minutes. Give a small "blip" to let it settle. If it is having a hard time staying running you may have to get an assistant until you can get to the front of the car. Now open or close the air bleed screw (CCW opens) next to the IAC until the car idles at 575 to 600 rpm. For guys with aftermarket cams and an EEC tuner, you might want to idle a bit more briskly, say 650 to 675.

Turn off the car. Now count the number of turns clockwise to close on the idle air bleed screw. If it falls between 1/2 and 2, it's okay, now reverse it out the same number of turns. Log the number somewhere in case you need it for the future. Reconnect the IAC. You are done.

If the air bleed screw is above 2 turns, it's a good idea to tighten the idle stop screw another 1/2 turn, then repeat the idle setting. If it is below 1/2 turn, then loosen the idle stop screw by 1/4 to 1/2 a turn, and repeat the idle setting. Be sure to put another drop of silicone rtv on the stop screw if it was disturbed. Reconnect the IAC. You are done.