Question about 1999 Chevrolet Cavalier

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1999 Z24 runs rough when warm

My daughter's Z24 with 2.4L 4 cylinder runs rough and hesitates when at part-throttle. Under full throttle and idle the car runs smoothly.
This car does not have plug wires, rather a coil housing under an engine cover. The coil housing showed continuity from each coil pick up to each spark plug connector; I think it is ok. Installed new plugs. Replaced one of the coil packs: 1 looked newer than the other, so I replaced the old-looking one. I did use the dielectric grease on the 8 connector springs. The local parts store cannot check the ignition control module and a new one costs $170. Anyway, my question is what should I be looking for to clear up this hesitation? Thank you for any help you can provide.

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  • 14 more comments 
  • swvogt Jan 09, 2009

    it misses but does not backfire. It does not do this at steady speed, only when accelerating from a stop, unless I really stomp on it.
    Where is the tps? Thanks for the help!

  • swvogt Jan 14, 2009

    Well, I put another new coil as well as a coil housing and it runs like a top. No more hesitation or missing. According to respected sources, don't waste time on diagnosing on a QuadIV until AFTER the coil housing has been replaced. They are bad for cross and misfire when they age.

    Just out of curiosity, how do I check the tps? I can remove it and replace it, but there does not appear to be a shade tree technique to check it.

    Thanks for the help!

  • swvogt Jan 15, 2009

    Well, there is still a slight and occasional hesitation. I'll see the
    car Saturday and give that tps a test, as you recommend. I am worried
    that the ignition module is the problem, though. Local vendor said I
    could try one and see whether or not the problem is resolved. The im
    is an expensive little puppy.

    It seems a shame that the ignition module and coils are right in that
    upper valley. It seems to me that this area would be about the hottest
    place to put these electronic components, especially with what amounts
    to a closed oven door on top, even if it is aluminum.

  • swvogt Jan 17, 2009

    The car has developed quite a bit of hesitation since my last "repair" effort. So today, while my little girl came over for lunch, I checked the tps, seemed ok, but tried a new one anyway. The car continued to hesitate. So I put the old one back on. Since she had to go, I was unable to try the ignition module changeout. What a downer.

  • swvogt Jan 18, 2009

    The advice I have received here is very helpful. It is great getting
    all the support. Funny thing is, my daughter is taking an auto repair
    course at the University starting the 27th; she will learn just how
    ignorant her father is about cars! And she can change the filter herself and try the gas line anti freeze herself.

    I have put a vendor code reader on this car and no codes show, at least awhile ago, but not this time.
    Thanks for all the help! I'll post what fixes it.

  • swvogt Jan 18, 2009

    What about STP fuel injector cleaner? I have a couple pints of these.

  • swvogt Jan 25, 2009

    Well, now an update. When it is hesitating up a hill or during acceleration, I put it in neutral and rev, and the motor revs fine. Looking for the infernal transmission lid now.

  • swvogt Jan 25, 2009

    Well, now an update. When it is hesitating up a hill or during acceleration, I put it in neutral and rev, and the motor revs fine. Looking for the infernal transmission lid now.

  • swvogt Jan 26, 2009

    Didn't find the infernal transmission cap. Couldn't find the fuel filter either. Pretty sure we were close:). The car is pretty small. I still say take it to my mechanic or wait to talk to her professor. I am certainly curious. Thanks for all the help.

  • swvogt Feb 10, 2009

    Well, dirt and gunk is the enemy. Cleaned the IAC, lot of buildup on sensor end and mounting hole/inlet, cleaned the MAP(MAF?) sensor inlet, vacuum tube, cleaned throttle body bore, all vacuum inlets, EGR sensor(?) on front of valve body, there was a LOT of gunk on the business end of that baby. Cleaned the AIT in the tube between the air box and the throttle body. Found no cracked hoses. I took it for a spin, and it seemed a lot better, no hesitation or bogging. We shall see over the next couple of days, and I will update.

    When I first started out on the test drive, the engine did not seem to know what speed to run, almost like high idle on a carbureted engine. Maybe just because it's a little chilly here, about 51°F. After about 1 mile, driving idle settled down, and sitting still in drive the idle was a pretty smooth 600 rpm by dash tach. I feel a few sporadic misses, I expect that to go away, or I might read the plugs.

    Thought I would mention that I did indeed try a new ignition module previous to the above effort. The old one tested bad, so I had high hopes that $185 would be well spent. The hesitation was markedly less, but still there, especially when turning left. So I returned the new unit, those guys are the best. They will continue to get my business.

    The tranny inlet cap/check thingy is still not found, but shifting is smooth and there is no slipping, so not an immediate issue.

    My thanks to all those who took the time to read and respond. Steve

  • Anonymous Feb 10, 2009

    I have the same problem with mine at high idle it is smooth but after it warms up and idle drops to about 600 rpm I get a rough vibration like a miss-fire I've recently changed plugs, changed the coil pack, changed the rear O2 sensor, about to change fuel filter. Although I think it's a vacuum leak.

  • swvogt Feb 25, 2009

    still bogging down. one of her professors thinks it might be the power steering sensor. I can't find any info about the effects of a failing power steering sensor. Any comments would be greatly appreciated. BTW, she changed the fuel filter, and that had no effect on the problem. Steve

  • johnnovicki Apr 15, 2009

    I have a very similar problem with the engine "hesitation", especially when giving more than about 50% throttle, and between 2500 and 4000 rpm. Any help would be appreciated.

  • johnnovicki Apr 15, 2009

    I'd be interested to hear also if the problem has reappeared, as I have headed down the same road as you, but have yet to find a definitive answer.

  • swvogt Apr 16, 2009

    It has been FIXED! I took it to a local reputable mechanic. After 3 days of working on it off and on, he called a guy in who put that baby on this fancy diagnostic computer and BAM! Found short in wire going around or near the air conditioner on the right side. The mechanic repaired the wire and only charged me his out of pocket on the electrical guy. Runs very well.

    It would hesitate turning left or straight, but not when turning right. In retrospect, it was virtually yelling at me what the problem was. The engine moves against the wiring harness as the car would turn left, but not right. Taking it to him was worth every penny. Less than you think, I bet.

    My thanks to all who helped above, certainly the efforts resulted in a nicer running car.

  • Roberta Smith
    Roberta Smith May 11, 2010

    Does it feel like a miss ?



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  • Master
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Buy a couple bottles of gas line antifreeze.... the coil would have been my first suggestion... but it sounds like you have water in your gas as well.... gas line antifreeze is alcohol (not the kind you drink) it sucks up water tho.


Posted on Jan 17, 2009

  • Roberta Smith
    Roberta Smith Jan 18, 2009

    if it has alcohol in it ... read the label.



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  • Chevrolet Master
  • 6,982 Answers

I'd check the throttle position sensor before going anywhere else. Your problem is right in the middle of the rpm range, right where the most wear on the tps happens.(assuming a 2,000 rpm average crusing rpm) An ignition or fuel problem generally shows up first at high rpm's where the load is greatest.

Posted on Jan 09, 2009

  • 6 more comments 
  • Richard Scordino Jan 09, 2009

    TPS is on the throttle body at one end of the 'butterfly" shaft (plate that opens to let in air, attached to throttle cable). usually has four wires attached to it.

  • Richard Scordino Jan 14, 2009

    There is a test that can be done with a digital ohmeter . It's listed in most good manuals. If you know anything about electronics, basically a tps is a variable resistor. As the pedal moves the signal changes to the ecu telling it what position it is in, then the ecu combines this info with other stuff from other sensors, then "decides" how much fuel & timing to add or subtract to match speed & load.
    I've found that the internal contacts wear in the area where the throttle sees the most use, translating to about 1500 -2200rpm. my test is to check that there is no break or "stutter" in continuity at this point. If the results iI get are questionable I go to the factory test. (I'm only right about 95% ot the time) PS if I had remembered you have a quad 4, I would have recommended to change that housing as well. I keep a good one hanging on the wall just to check this stuff. Generally though, it shows up more like a coil (high speed miss or miss under load) Glad you fixed it though

  • Richard Scordino Jan 15, 2009

    If vendor is willing to loan you that part, makes sense to give it a try...
    I can't figure out what the engineers are thinking when they locate electronics or sometimes even rubber hoses in extremely hot areas...And, they are designing this stuff on computers that need to be temp controlled so that the processors etc dont burn out! Would they mount their towers on top of a radiator??? 'Think not! The insanity of all this is that it has been going on for as long as I can remember, not just computers, but "new design changes" to items that worked perfectly before they messed with them! All this stuff adds to the price and reduces reliability! When you "nail down" the problem, post the answer. 'Been in the business a long time and am still learning!!

  • Richard Scordino Jan 17, 2009

    One of the great disadvantages to "remote control" repair is that one cannot rely on the full range of senses that one develops without even being aware of it while engaged in "hands-on"repair. Since you did not mention fuel, I focused upon the direction you were going. And it made sense. However, seeing that your problem seems to be slowly worsening, instead of improving, I would recommend that you take a moment to regroup and take a good look at the fuel side of this.(both ign and fuel sometimes have nearly identical symptoms. Also, instead of guessing, see if you can either borrow or have someone use a scan tool on the engine to see what codes if any are in there. (some of the "supermarket" type parts houses will read your codes free, in hopes of selling you parts.) For a start, I would make sure the fuel filter is not more than 1yr old. if so, regardless of symptoms, it should be replaced as routine maintenence and therefore taken out of the equation. Sorry the tps did not help... I've tested tons of them and generally on average, that has been the source of at least 80% of the problems I've seen like yours.

  • Richard Scordino Jan 18, 2009

    Do not use gas line antifreeze. Most available fuels now contain at least 10% ethanol... All alchohols are hygroscopic (pull in moisture)... More can worsen performance. If you want to put anything at all in there, I'd use 3oz of acetone per 10gal gasoline, with a 1oz marvel oil chaser. This will not harm components and will help clean injector nozzles.
    Im going 10-7 on this one and await your final cure!!

  • Richard Scordino Jan 26, 2009

    You are going astray with the transmission : A miss under load will quite often disappear when load is removed. (has to do with working cylinder pressures) Transmission can react to load, attempting to "balance " available power to load applied, but it is reacting to not causing problem! PS: just a thought: re-check the temp sensor...sometimes if not reading temp I have seen them cause an over-rich condition, if it "thinks" the engine is still cold! Still, have you gotten any codes yet? Have you checked to make sure the basics (compression, etc.) are correct?

  • Richard Scordino Feb 10, 2009

    Really glad to hear that it is running better. Often, I neglect the basics (cleaning stuff) when I post answers here. (though while doing hands on testing I always do that as a "given") It's nice to see someone actually post the result of their experience after it's fixed...too often they gust go away. With over thirty years in business, I'm still learning...It never stops!!!!.

  • Richard Scordino Feb 25, 2009

    Can't believe your'e still doing battle with that thing...since your last post I figured you either had it fixed or burned it down!!! good to hear you are making progress...might be a good idea to go back over some of the stuff you cleaned...sometimes stuff that got loosened up can't find it's way out of the system. The problem you had at first after cleaning is that the computer was re-setting operating parameters. Shows that you did the right thing...Didn't think anyone but me read plugs anymore (it's harder now 'cause the computer tries to cover up everything). When you're finished, post again!!



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