Intermittent idle stumble and rough running

[tfvesquire]

I understand there have been several threads and post on this issue an most of the time it ends up either being the MAF or a coilpack going bad. I just wanted to post my experience on this issue with my 98 Q and what I ended up doing before I started replacing too many parts. I had a terrible idle stumble shortly after I installed my replacement salvage yard engine and I was not sure if the mechanic who did the swap bumped or dropped my MAF and damaged it or if there was a bad coilpack or injector. After the car kept dying I tested the MAF and it was bad so I replaced it with a low mileage sensor off a 2001 Q. Car ran great.

Everything seemed to operate smoothly for several months when I started getting a stumble at idle, not the point of stalling like before, but it was more than annoying. I did the research and found other members with the same issues and the common fix was to start replacing coils. I also ran fuel injector cleaners in the tank (Chevron Complete Fuel System and Redline) and got some postive results. I replaced the fuel filter in the process. I can saw that after running about 8 cans of pour in fuel injector cleaner, I am starting to see some consistent positive results leding me to believe that one or more of the injectors must have been coked up or had some hard deposits that broke free and were intermittently interupting the fuel flow. The reason I think is that when it would start to hiccup at a stop light and run rough, after I parked and turned the car off and immedately started in again, everything ran smoothly. I guess the tiny deposits needed to get broken down, dissolved and eventualy blown thru the tiny injector orifices. I chose to start the intense cleaning of the injectors, in lieu of pulling the injectors out and having them ultrasonically cleaned and used the cleaning solutions with the highest PEA ((sp?) levels. Plus, I have read about issues with injectors not sealing properly after removal leading to other emission problems due to leakage.

I just wanted to post this for others to consider before they start spending needless monies on replacement coilpacks only to have the same symptoms reappear. For me, it took more than one or two applications and a mix of town and high speed expressway driving to start to remove these deposits. I can definitely say they don't go away easy since it took thousands of miles to build them up. Don't forget to change your oil during the cleaing process!! But I can say that depending on how bad your injectors are, they can be cleaned if you are diligent about it and don't give up. I think most on here would agree that nothing is more annoying or embarassing that your car shuddering at a stop light.

Take care.

Ted

[Gumbymonster]

Hi Ted,

I just bought a 99 Q45t last month. It has been giving me the same symptoms. So far, I ran one can of seafoam through the tank. Would you recommend running some through the vacuum brake line?

Thanks,
Mike

[tfvesquire]

Hi Ted,

I just bought a 99 Q45t last month. It has been giving me the same symptoms. So far, I ran one can of seafoam through the tank. Would you recommend running some through the vacuum brake line?

Thanks,
Mike

Hi Mike:

Sorry, but you will only be cleaning the upper intake "air" passages, not the fuel injectors or fuel system. It won't hurt to clean the air intake as well, but plan on cleaning the IAC, TB and butterfly plates and checking both PCV valves to make sure neither is stuck shut (check ball should move freely when you shake the PCV.

My suggestion is to not assume the prior owner did anything you can rely on and do everything yourself. That way, you have a good startign point to diagnose any idle or performance issues.

Ted

[Gumbymonster]

Thanks Ted!

One other thing. Do you know of anything I can do to replace the front struts and/or cartridges on my touring 99 Q45t? It seems like the only thing I am able to do is buy the struts from the OEM at $1,000+ for the front pair.

Thanks,

Mike

[QueenV]

I've had the same problem with my '97. Rough idle at stop lights in drive. I can make the idle smooth if I put it in park. I put Red line SI-1 in it, full bottle per tank, and the rough idle magically smooths out for the whole tankfull. If I don't put red line in, the car is has rough idle again. Half a bottle is not good enough. I'm on my 5th bottle of Red line and at some point I'd like to wean my Q off it. What is the best thing to do? Should I buy the fuel injection cleaning service some shops offer? I am fairly clueless as to which way to proceed.

[chipahoy]

i recently changed my valve cover gasket on the driver side and after putting everything back together it was idling rough. i took it for a test drive and i though maybe i had reconnected the plug wires incorrectly but they are pretty idiot proof. i replaced the plugs, and still have the same issue. im sure its ignition related as it ran smoothly until i did the work. my next step is to check the coils. fortunately both the price of iridium plugs and ignition coils are pretty cheap. i got the plugs, 4 ngk iridium's, for $28 delivered and coils can be had for <$100 for all 8 on ebay/amazon.

[94Q45Beast]

first of all its better the do both valve cover gaskets at once, if one side leaks then the other isn't too far behind, second, check all connectors, clean and grease them, also make sure your connectors on the ignition control module and the coil packs and are all the way in and clicked. then check fuel hoses for loose clamps and leakage...did you remove the plenum to do the VCG?

[chipahoy]

i recently changed my valve cover gasket on the driver side and after putting everything back together it was idling rough. i took it for a test drive and i though maybe i had reconnected the plug wires incorrectly but they are pretty idiot proof. i replaced the plugs, and still have the same issue. im sure its ignition related as it ran smoothly until i did the work. my next step is to check the coils. fortunately both the price of iridium plugs and ignition coils are pretty cheap. i got the plugs, 4 ngk iridium's, for $28 delivered and coils can be had for <$100 for all 8 on ebay/amazon.

[94Q45Beast]

I take that back, I read your other post on another thread and you used iridium plugs....that's a big no no for the Q's...that could/may/is/possibly be your idle issue, only use NGK Pfr-5g-11, I got all 8 plugs for free because the ones I pulled off during rehab had a 90K mile warranty. and OEM Coils....after markets are cheap for a reason other wise I would have bought a bunch of spares by now since I can get them for a few bucks a piece (don't need to, my coil packs are in excellent condition) along with an aftermarket platinum plug for another few dollars.

[qship96]

Nothing wrong with using NGK iridium plugs in the Q, not really needed though as the standard ngk platinum plugs already will outlast the valve cover gaskets,and easy to replace plugs while doing the gaskets.

[94Q45Beast]

while reading some of pops notes in my Q's file, I remember him stating that the NGK pfr-5g-11's fouled when he reached his destination on a road trip to canada and temporarily put some NGK iridium plugs in and drove all the way back to ATL with a stumble at idle and a loss in power. and the idle and power issues that were resolved when he finally got his hands on some NGK double plats.

[QueenV]

The previous owner said he replaced the plugs. I'm guessing since I bought the car for $1200 that he didn't replace them with NGK double platinum. I'll add that to the "project" list.

[chipahoy]

Thanks for all the great tech tips. I don't think its an injector or manifold related issue; as i said in the first post, the car ran great, like a scalded dog. it idled and ran fine prior to changing the valve cover gasket but im one of those guys that cant stand any leaks in my car. yes, i also plan on changing the passenger side gasket too, but one side at a time is about all i can handle. if you have done this job before you know what i mean. Anyway, I have owned this car since 2000 and have always used the iridium, in fact i think they are standard install for the "T" model. Tonight I plan on connecting the diagnostic gauge to the OBDC II port and see what kind of readings i get. I also have an old Mercury spark tester (from my marine mechanic days) and will check each cylinder for fire. I am still waiting for the ignition coils i ordered to arrive.

[chipahoy]

Nothing wrong with using NGK iridium plugs in the Q, not really needed though as the standard ngk platinum plugs already will outlast the valve cover gaskets,and easy to replace plugs while doing the gaskets.

But it's a lot easier to replace the plugs than the valve cover gasket....

[94Q45Beast]

my 94 is OCD on parts, they have to be OEM or FSM specified otherwise I run into problems, unless its something that doesn't require a power source. your FSM should give you a series of diagnostics tests to perform based on your trouble code or symptoms to help source the issue. I doubt iridium plugs are OEM grade, but if it work for you without problems then great.