97 achieva 2.4 rough idle

[Rogueknight]

Ok here was the mother of all issues I have ever dealt with. I have seen several post on different boards but noone really showing the solution so I am posting this to let everyone know my expierience and hopefully help you out.

Ok I bought the car with a rough idle on it and only getting 20 mpg. It seemed to run fine soon as you gave it gas but at idle it would shake and click a bit. As I do with any car I buy I consider no maintenance has ever been done. So I change the standard:
Transmission fluid/ filter
Oil/ filter
Spark plugs (originally put in Bosh Platnum plus 4)
Air filter
Fuel Filter (I REALLY hate that quick disconnect)
wiper blades (love Bosh microedge)
flushed coolant
Rear shocks Monroe sensatrac

Anyway after all that I still had a rough idle.
So now I start digging into this problem (no check engine light but can pull code for random missfire p0300, O2 sensor bank 2, running rich, running lean)
I change:
Coils
spark plug isulators
Both Oxygen sensors
cleaned idle air control valve
throw some gas additive in

I then ask a couple mechanics about the car trying to figure out what best to check next.

I then take it to the Chevy dealership and get the ignition recall done. They didn't give me too much confidence and took 2 months to get part.

Now I take the car to the Pontiac dealership (no more olds dealerships) and I submit the car to them cause they talked a good game about how precise thier diagnostics are and how they could tell me for sure what was wrong so I wouldn't just be part swapping.
Boy that was an issue. I have to give them props though cause they did find the coolant smell was from this plastic piece that goes in the engine and has like 4 things that connect to it. well it was deteriorated on the inside and it has such a minor leak you never found the coolant just smelled it all the time. So they changed that part out. they Also found the coil housing has a small crack in it and told me I needed to change it. Well I didn't see how a crack on the side of the plastic would do it but ok I changed it ($85 part, wasn't paying them 130 to put it on). They also told me Bosh plugs don't work well in GM cars and that I also needed to put AC Delco Platnums in. But then they said everything else checked out good and all electronics check good. Didn't get them from there O'Reillys was cheaper for the same part, they have seen a lot of me lately lol.
Anyway at this point changed:
Coolant housing
Coil housing
put in the AC Delco Platnum plugs

Car still idles rough and still only 20 mpg.
durring this weekend I charge the AC system up and then put Thermoquiet pads on the front brakes. I also got the Fuel injectors cleaned.
Now on my way to college that Monday morning a new bug pops up, the car has a hickup. at random while driving the RPMs drop about 3-500 just momentarily and then drives fine. There was no rhyme nor reason so the hickup, you could sometimes drive 10 miles without a hickup or you could have 5 in two miles. Then it had a big hickup and the Cruise went off and check engine light came on and stayed on. Went and had the codes read and it said crankshaft sensor. Drove the car back to the city I live in and it was still a very intermittent problem so I drive straight to the dealership. Parts guy didn't think it was a crank sensor cause then it wouldn't have run if it was. But they didn't know off the top of thier head what it was. So after work I get a crank sensor at Autozone and come home and go to put it in (really two ways to change that thing either remove the intake manifold which I didn't wanna do, or jack the car up, go underneath and remove the oil filter and then the crank sensor is just above the oil filter) that works if you can work by feel cause you won't be able to see squat.

Anyway, started the car, rough idle and after the car warmed up sure enough there was the hickup. The hickup kept throwing a code for a crank sensor. I was also now getting a code for a camshaft sensor. I changed that out and no good still throws code for crankshaft sensor.The wierd thing about the hickup it seemed to only happen after the engine warmed up and usually when going uphill or when a load was on. So I swapped out the EGR valve, no help. So back to Pontiac I go.
Pontiac has my car all day and when I came to get my car they said they were stumped and had no clue what was going on, it would do the same thing for them if they took it for a drive but would never do it at idle or sitting still. But the dealership said they give up they don't know whats wrong with the car but they said it could be the autozone part, so I pick up a crankshaft sensor from the dealership and go home to put it in.

To my surprise when I got home my factory service manuals I ordered had come in that day. I changed out the Crankshaft sensor again and then started her up and still rough idle and hickup not even 3 miles down the road. I read up in the factory service manual and there is a wierd learning proceedure for the computer anytime you move the crankshaft sensor even if you remove it and put it right back. The dealership didn't know about this but I took my factory manuals in and showed the the proceedure (you have to have a tech II computer to do this proceedure) and let them use my manuals to get it done (another $65).
It didn't help.
So now I am checking wiring one wire at a time, I am ohming out every part I can find. I try swapping out Idle Air control valves and ignition coils and bought a vacuum tester and test all the vacuum readings. Everything checks good but still idles rough and has a hickup. So then I dig a little deeper, I pull the intake manifold and clean it out, clean up the intake valves, and clean out the throttle body.
No good.
So now I turn to Vacuum leaks. I gut out all those hard tubing vacuum lines (I hate those things, they get hot and deteriorate SO fast). In the process of doing this thanks to the factory service manual I discover another problem. There is a check valve placed right in front of the vacuum modulator which shoulnd't be there. So that gets chucked and all vacuum lines are replaced excpt the AC heater control vac line that goes into that big wire bundle but I had vacuum inside by the PCM.
Started the car up no go it was still rough idle and hickup if I drive anywhere that was getting worse it seemed.
Getting extremely frustrated I then turn to the transmission for the hickup problem as it seemed more vital.
Took the car to Ammco, and that was a joke. They said yeah the transmission needed to be rebuilt but they couldn't guarantee it would fix it cause it keeps throwing crankshaft sensor code when it hickups. Well I don't think they looked at it more than 5 min even though they kept it all day. I took it back and I put some brake fluid in the transmission (not much just a little) cause that will clean up your transmission. Still no help. So at this point I am still looking at the tranny and I pull the fluid out to make sure it isn't being contaminated nor have a coolant leak into it.
Extremely frustrated it's nowMonday and I go and have the muffler and Catalytic converter changed (they said this was clogged and broken internally) in case it might have been back pressure ( I couldn't get the ehaust manifold bolts off at the pipes to just try that). Now new Exhaust and still rough idle and intermittent hickup.
Ok now I am getting mad and down to 13 MPG lol.
So I take it to a couple shops and they refuse to take it after they hear the history of this problem. I found one that would take it but they wanted to do thier own diagnistics so I set up to drop the car off Tues morning. Well I never made it.
Monday evening at 10 pm I went to move the car and when I started her she made this lound metal sound that I didn't like. So that was it the car wasn't moving til fixed. I tore into the engine yet again. At 6 AM (yes worked all night long) I finally found it.
:!: The timing chain tentioner was dead and the chain had jumped a tooth on the exhaust cam. :!:
Not only that but someone had installed the wrong tentioner to begin with and though the Haynes book (which showed this tentioner as the old one on 91 and earlier models) said it was spring loaded. There wasn't a spring at all. So I got the correct tentioner from autozone and installed it. I put the car back together after moving that exhaust cam back a tooth and she purrs like a kitten.
Took her for a drive, no hickup, sitting at idle she is smooth as a babys butt. So after all that, thats what it was, timing chain tentioner and a cam off a tooth. A couple other mechanics I told seemed surprised cause the car only had 72000 miles on it when I got it (just under 74000 now), but after the two month fiasco I am glad it is finally over. Good luck and hope this helps more people out.

[jeremy96gase]

Damn dude. A set of tires, struts, new brake pads, and it'll be basicly new.

Are you going to flush the break fluid out of the trans?

[Rogueknight]

well the front tires and pads are new, hadn't messed with front struts yet lol.

I already flushed the tranny fluid again, you don't have to though you don't add much brake fluid to the tranny no more than a couple oz and it just acts as a cleaner additive and doesn't hurt the tranny. I had anyway just cause I was looking for signs of something in the fluid.

[SoLid_PrAnkstA]

man, i wish i'd known you'd solved it before i read that novel :p

[Josh]

congrats on finding the problem.

[darkfox]

Originally posted by Rogueknight
They also told me Bosh plugs don't work well in GM cars and that I also needed to put AC Delco Platnums in.

AC Delco plugs are definately way to go. Iridium plugs also work well.

Originally posted by Rogueknight
There is a check valve placed right in front of the vacuum modulator which shoulnd't be there.

uh yeah it is. All 2.4 auto's with the 4t60e have that little check valve. now put it back on.

Originally posted by Rogueknight
Took the car to Ammco, and that was a joke. They said yeah the transmission needed to be rebuilt but they couldn't guarantee it would fix it cause it keeps throwing crankshaft sensor code when it hickups. Well I don't think they looked at it more than 5 min even though they kept it all day. I took it back and I put some brake fluid in the transmission (not much just a little) cause that will clean up your transmission.

Yeah i've learned not to take my car to a lot of places. They will say yeah it needs work just because they want money.

Never heard of putting brake fluid in the tranny.

Originally posted by Rogueknight
:!:The timing chain tentioner was dead and the chain had jumped a tooth on the exhaust cam.:!: Not only that but someone had installed the wrong tentioner to begin with.

for some reason not a whole lot of mechanics know how to work on quads. :rolleyes: they tend to break them more than fix them. I don't know why this is... if they would bother to learn how the engine works its not to hard to figure out. :rolleyes:

[Rogueknight]

In the factory service manual there is a not about the vacuume modulator and it said in big bold letters (I'm not kidding or exaggerating) DO NOT hook up with the black and white check valve, transaxle damage may occur.
That is why I took it off. If it needs to be there ok no problem but I don't trust the dealership, they don't seem to know as much about the car as I have even learned and the main thing I was going by is the factory service manuals for the 97 achieva (two books). If I am not mistaken the check valve was even installed where it stops the vacuume and would then make it useless. Maybe mine had been installed backwards, I dunno.

[darkfox]

i dunno. every 2.4 auto i've seen has that, including mine...

uhoh. maybe GM screwed up lol.

[jeremy96gase]

Originally posted by darkfox
uhoh. maybe GM screwed up lol.

I wouldn't put it passed them;)