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Discussion Starter #1
Hey Guys. For the last week or so my engine has been doing a wierd a sort of shudder when at idle. The engine will be idling nicely at ~750 like normal and then it'll drop a little and make the car shudder and then it will surge back up to about 900 then drop to 750, stay there for a bit, and then drop and shudder and do it all over again. Logically, it shudders more often and harder when I have the AC on. I had it idling in the driveway and it did it, but it does it worse when actually driving it. The oil is good and right on the mark, same with tranny fluid and coolant. I checked my CAI and everything looked good and I don't think there was anything wrong with it in terms of oil getting on the wire. So I'm rather baffled. I have yet to pull the plugs though, but I did change them at 30K and gapped them all right at .044". It also doesn't seem to have any lose of power when actually driving it, just a shuddering and low idle.

I've got no CEL light, but would it maybe put a code into the computer but it's not bad enough to throw the CEL light but reading the codes would show something's not right? I'm also getting slightly worse gas mileage, which may or may not be linked, but if it was, I would think that it would cause a problem all the time (like a missing plug) and then throw a code. Any thoughts guys?

-mobiuslogic
 

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Could be the IAC. Also, make sure your EGR valve isn't stuck open.
 

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Discussion Starter #3
Originally posted by dIESEL600@Jun 16 2004, 01:42 PM
Could be the IAC. Also, make sure your EGR valve isn't stuck open.
:bump:

Wouldn't both of these throw a code? I'm sure the EGR should considering it's an emission item.

-mobiuslogic
 

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I was having the same problem last fall.

The spark plug was looking ok, but a mecanical has changed all the 6 plug for brand new and it was not some normal plug, it was 3 or 4 $ over the other (maybe some high-performance plugs) but I dont remember the label.

And now all its okay
 

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Originally posted by mobiuslogic+Jun 16 2004, 10:33 PM--><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (mobiuslogic @ Jun 16 2004, 10:33 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-dIESEL600@Jun 16 2004, 01:42 PM
Could be the IAC. Also, make sure your EGR valve isn't stuck open.
:bump:

Wouldn't both of these throw a code? I'm sure the EGR should considering it's an emission item.

-mobiuslogic [/b][/quote]
In my experience with these cars a problem has to be pretty bad before a code is thrown. Especially with EGR, unless the DPFE sensor goes bad (which is often the case), it takes alot to throw a code. I have driven with the EGR line plugged, with the EGR forced open, etc., without getting a code.
It's probably not the cause of your problems, but it is an easy thing to rule out.
 
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:withstupid:

Also, clean the MAF wires anyhow. I doubt that it's a plug, or anything ignition related, since the car drives fine.
 

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Discussion Starter #7
Yeah, the car drives fine, plenty of power, it's just at idle. Like I said I have gotten a slight loss of gas mileage which may or may not be related. But, how would I go about checking the EGR valve and also cleaning the MAF wires? As for spark plugs I put in Bosch platinums, not Motorcraft. However I'm also leaning away from ignition because I put the plugs in 10K ago and just now started getting this.

-mobiuslogic
 

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There was a recent thread about people complaining about the Bosch plugs. May be related. You might also try adding some fuel system cleaner additive. Maybe it's a fuel system problem. Watch out for your fuel pump failing. I've replaced mine on my 2000 twice already. May also be a coil failing. Remember 2000's have Coil on Plug ignition. I had two coils fail on mine as well. Probably within 9 months to a year of each other. Haven't had a problem with them since they were replaced. Usually if they fail, you get a very slugish engine though I here. I'm not sure though, cause when mine failed, I just noticed the engine was surging and I didn't try pushing it hard cause I didn't wanna break something. I just made it home with it and got it to the dealer for repair. Maybe check compression on all your cylinders? Beyond that, I don't know.

-Dan
 

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Is your A/c on when it does this? mine does the exact same thing at idle when the a/c is on. When its off, it idles without a problem. If its not that, then do what ^^^they^^^ said.
 

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My Pontiac did the same thing. Had power just idle. I pulled the plugs at 42k and that were not pretty. That were gap all wrong. They were to be set at .55. But they were some thing like this. .50 .58 .52 .53 Thank-You gm <_< I put some ac delco rapid fire 4.19 each ouch I did not want to spend 5.99 on the platinum plugs that were in their. After that and a new air filter my problems were gone. I say spend the money and get some Motor Craft 605PP $4.49 each

some more notes
All gm cars i believe after 94or95 came from the factory with platinum plugs. Even the little crappy 2.0 had em. Most of the gm motors need a hot plug that why Bosch is not a good plug for the engine.

Also my car only did that to wih the a/c on at like a red light
 

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Make sure your Idle Control Valve is attached properly. When I removed my pendulum to clean it and then reinstalled it, I thought I attached my ICV valve fine, but it wasn't on all the way. It idled really bad, until I figured it out.

This is a good tip to remember. To avoid dirt particals to get into your wire plugs, put electrical tape over it when ever you pull out any plugs to do something. It's possible to get dirt into the plug and cause your sensors and wires to not connect as they should.
 

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Discussion Starter #12
Well thanks for the help so far guys. It's a Vulcan though, so I have a coil pack, not Coil on plug, and everything seems to be firing fine. If I had a coil die, I would be losing power on 2 cylinders because each coil fires 2 cylinders on the vulcan, 1 is at the top of compression, the other at the top of exhaust, then they switch. But I would likely notice 2 out of 6 bad cylinders as way more than a slight shudder. Plus it's only at idle.

I never pulled the IAC but I'll check it out. How about cleaning that MAF?

-mobiuslogic
 
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Disconnect the air intake hose, and use some contact cleaner (without lubricant) to clean it. Spray the wires well, and let it air dry.

Also, a vacuum leak will do the same thing, although that should throw a lean code on both banks.
 
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