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Chevy Suburban/Tahoe Rough Idle and Stalling



  • Sorry, but I fail to see how a "starter" can effect the way an engine runs. After the engine starts, the "starter" has no further function. The starter gear slides back into its shell and waits for the next engine crank. Do some starters perform an additional function that I am not aware of? Thanks.
  • woodyjwoodyj Posts: 6
    My wife and I purchased a 2003 Chevy Suburban. At first, we had no problems until we had the vehicle for a few months. We ran the ODB II diagnostics and found several cylinders misfiring, and injector circut malfunctioning. We then took it in to dealer to have it further diagnosed and fixed. They did their thing and replaced one injector wire at first, but that did not fixed the issue. Problem reoccurred after we brought the vehicle home. So we took the Suburban in again and they said they had to replace 3 more injector wires. They did that, and everything was fine until another week passed. Same problem again. I got tired of the run around and didn't have the patience with the dealer, or the money we were throwing away. I did simple check of sparkplug, sparkplug wires, fuel injector wires, and to my surprise it was the main ignition coil connector wires. I ended up splicing up the wires together. I did more checks inside the wire jacket that leads back to the main computer in the engine. Found more wires that were worn down to the copper. Seems like either prior owner or dealer tried to fix the problem and couldn't find the main issue.
    So now, my Suburban runs fine.
  • pear69pear69 Posts: 20
    Don't know if you solved this problem, but YES 87 octane gas will cause this problem. Octane is an additive that is put into gasoline to reduce the spontanious combustion that happens when gasoline is compressed inside of the combustion chamber. The lower the octane the higher the chance of spontanious combustion. This is bad because if gasoline combusts (fires) before the spark plug ignites the piston will be on the way up in the cylinder. This is what is known as a "ping" or "detonation". A "ping" will eventualy destroy a motor.
  • I have a 99 Suburban with a 5.7. I had a leak on my intake gasket and got that replaced. After a week, engine runs rough and showing P0300. Replaced cap/rotors, plug, wires, MAP sensor, Cam Sensor, and Crankshaft sensor. Then I replaced the ecm. Still doing the same thing. Mechanic advised me that it can be the head gasket that will run be about $1200 to $1500. I don't think thats the problem. I did not let them fix the head gasket. After I replaced all the things that I replaced, now its showing p0304 cylinder misfire on 4. Please help if anyone solved the problem. Can it be my EGR valve, fuel injector? I checked the plug on cylinder 4 and it is firing fine.


  • kiawahkiawah Posts: 3,666
    You could have a bad head gasket around cylinder#4, right?

    Have any compression tests done??
  • pear69pear69 Posts: 20
    It is very important that A/C delco spark plugs, and spark plug wires are used on these engines.  A p0300 is a general misfire and a p0304 is cylinder 4 misfiring. They both may or may not be related. Your engine has a problem that many people overlook, the distributer gear wears out--especialy after it is removed and put back in--as it was when you had the intake gaskets done. If the distributer gear wears too much it will misfire the engine. Also, the timing on your engine must be set with a computer scan tool, NOT a timing light--like in the old days. When the distributer was removed on your engine, it is almost impossible to put back in exactly perfect. This is a commonly overlooked problem also. A dealer is the only one who can properly time your engine. When the intake is removed from the engine, the injector electrical connector must be unplugged. This plug is very sensitive to damage. It is easy to bend the little pin that plugs into the injector. This could be the cause of cylinder 4 missing.Also make sure that all the ground wires are put back on the engine. The ECM fires the injectors by controlling the ground (not the hot or power wire). If a ground is off it could overload the ground system by putting strain on other grounds to pick up the slack. Grounds work just like power wires when it comes to overloading.  This also could be an intake leak. Start the engine and let it run for a while. Now, get a spray can of electrical cleaner ( CRC ) or brake cleaner and spray it around the upper and lower intake while the engine is running. If the engine boggs down or starts to run bad-and -- then clears up when you stop spraying---you have an intake leak. If this is the case the intake gasket was changed wrong...  The best way to determine if the head gasket is bad is to do a compression and leak down test on all cylinders.    If the plug looks fine then it is probably NOT the head gasket---do a compression test to be sure though....
    Your problem sounds like a leaking intake somewhere or most likely electrical.
  • I Thank you all for helping me out. It really helped me alot. I think I got it figured out. The engine has no Vacuum leak. The problem is my #4 fuel injector. I pulled the spark plug that I have installed 2 weeks ago and it looks like the injector is bad. I will be replacing my fuel injector assembly this weekend and I will let you all know the outcome. Cross my finger that the problem is solve. I finally had another mechanic take a look at it last night. He checked the vacuum leak, compression and he came up with a bad injector on cylinder number 4.

    Keep you all posted after this weekend.

    Thank you again.
  • pear69pear69 Posts: 20
    If you are changing the entire assembly I suggest installing the upgraded injector assembly. Your stock injector assembly is called a cpfi system--the upgrade is called mpfi. The only difference is that the injector itself is moved from the center of the assembly (stock location) to the port of the intake runner (upgraded location). The reason this is better is that it elliminates the (problem proan) poppet. If the 4 injector is the problem, then it is the poppet sticking --causing a "burp" in the fuel flow. I bet the 4 spark plug is all covered with black soot---carbon--isn't it?
  • Thanks for the information. I heard about the upgrade version and that is what I will be looking for tomorrow and I get the new injector assembly. I really appreciate all your help. I will keep you all posted by this weekend if I solve the mystery.

    You are very right. The plugs are only about 2 1/2 weeks old and I have pulled number 2 and 4 plug to compare and you are right on. The number 4 plug was black and the number 2 was perfect. I have also pulled the plug next to 4 and it was fine looking too.

    Anyway, I will keep you all posted and thank you so much.

  • pear69pear69 Posts: 20
    Go on Ebay type in sefi update and you will see the updated version of your injector assembly in DR. INJECTORS Ebay store...
  • I thank you again. I will check it out right now. Thanks and will keep you all posted.
  • I checked out ebay for the sefi update and that is exactly what AutoZone is giving me. They ordered it and arriving tomorrow for me to pick it up. It's about the same price.

  • Hello there! I have changed out the fuel injector and unfortunately it did not make any difference. It is still running the same. If I run the car with the MAF Sensor and when the car hits 40MPH that SES light blinks. When I run the car w/out the MAF sensor the SES will not blink and run better but you can still feel the miss-fire but not as much. The only time you will feel it is when you come to a stop and on an idle. Can an O2 sensor create a misfire? I have been reading a lot of forum with the same problems, has anyone fixed this issue? I am leading to the O2 or the MAF sensor. If I can't fix it, I have no choice to bring it to the dealer.
  • Hello Pearl69. I still need you wisdom. Can you help?

    Hello there! I have changed out the fuel injector and unfortunately it did not make any difference. It is still running the same. If I run the car with the MAF Sensor and when the car hits 40MPH that SES light blinks. When I run the car w/out the MAF sensor the SES will not blink and run better but you can still feel the miss-fire but not as much. The only time you will feel it is when you come to a stop and on an idle. Can an O2 sensor create a misfire?


  • pear69pear69 Posts: 20
    I'll help, but you must start from the beginning. First- before the intake gaskets were changed did the engine have this problem? If the ses light is on then there is a trouble code stored in the computer, what is the code? If you do not have a scanner Autozone-or a place like that- will scan the computer for free. If the light is not on, then wait until it is on and then take it to get scanned. The code is very important. When you changed the spark plugs and wires what brand of wires and plugs did you use? Did you install the updated version of the injector assembly?

    I will help all I can, but answer the four questions I just asked. Please do not change anything on the engine. You must start from the beginning and be patient, If not then do not waste my time. I like helping people but when they go off track and change things that do not need changing then all they are doing is wasting money and time. If you did change the entire injector assembly then that is good. Even if it didn't need it, this upgrade should be done anyway..
  • The intake manifold started to leak and had a mechanic work on it. No the engine was running fine. A week after the intake was worked on, I noticed that the engine was shaking and seems like it was fouled up going on an incline (hill) Drove the car home and it seems worst and the engine was rough. Went to AutoZone and got it scanned. First code was P0300. The guys at autozone said to replace the plugs, wires, cap and rotor which I did. Started the car up and there was no change. Went autozone again and scanned it. Now it showing P0304. They said it might be the cam sensor, crank shaft sensor, Map sensors. I bought all those and replaced it and still the same. Went back in to Autozone and showing the same code. My friend told me to look at plug number 2 and 4 and compare. 4 was blackish color and the 2 was clean. He said that he think its the fuel injector so I went to autozone to buy the new spide system. Replaced that over the weekend and no luck. I am running low on repair budget. I would to get this solve myself rather than taking it to the dealer. The car seem to run fine when cold but as it gets hotter you can feel more roughness. It also runs fine if the MAF sensor is not connected. If the MAF is connected and you go 40mph the ses light blinks. MAF disconnected, SES does not blink and able to drive more than 40mph.

    Thanks for your help.
  • Hello Pear69. I forgot to give you the brand yesterday.

    Spark Plug (Champion) Purchased at Autozone as well.
    Wires (Dura something from Autozone
    Cap and Rotors purchased at Pepboys (BWD brand)
    Map/cam/crank are BWD brand
    Fuel Injectors brand below. Purchased at Autozone.
    Gp-Sorensen / Fuel Injector
    Warranty - 1 YR 800-1513N $307.99

    I changed all these part after the Suburban start running very rough. First code was a P0300. After changing and installing the plugs/wires code became P0304 and after changing the rest of the part that I bought, the code remain on P0304.

    Thank you in advance for your help.


  • pear69pear69 Posts: 20
    I am assuming that the lower intake manifold was leaking when you say the mechanic replaced the intake gaskets.(there is an upper and lower intake manifold)
    If the problem was not existing before the lower intake was removed to replace the gasket then lets start there..... In order to change the lower intake gasket the intake must be removed. You must unplug (and tie out of the way) the entire engine wiring harness. The harness has important ground wires that must be disconnected to remove. Follow the engine wire harness and look for ground wires disconnected. One is connected to the coolant port bolt stud (where the upper radiator hose connects to the upper intake)-if this ground is disconnected the injector ground system will overload and cause your problem. If you find all wires connected move to this---
    The distributer must be removed in order to remove the lower intake manifold. Being that you had a P0300 code (a general misfire condition) the distributer gear could be worn out. Removeing the distributer to check this is not hard at all. If you changed the injector assembly then you can remove the distributer to check this.
    First (most importantly) bring the no. 1 cylinder up to Top Dead Center (TDC). To do this disconnect the battery-- take the air plentum off-- remove the spark plugs and wires--locate the timing pointer on the block (looking at the engine from the front it will be just to the right of the front timing chain cover--spraying some brake cleaner on the pointer may help if it is dirty)--turn the engine "by hand" and align the timing mark on the crank balancer up with the pointer (the balancer mark is a engraved line machined into the balancer)--now very very very carefully remove the distributer cap. On the distributer cap base (where the cap screws down too) there are two notches, one has a number 8 engraved on it and one has a number 6 engraved on it (look very close--use a magnifying glass if necessary). The rotor should be pointing to the number 8. Disregard the number 6 (it is for 6 cylinder engines). This is number 1 cylinder firing position, verify this by compairing the distributer cap to the rotor position;it should be pointing to the contact for cylinder one. If not simply rotate the engine "by hand" 1 turn, until the timing mark on the balancer comes around again--360 degrees. Now you are at TDC...The following is the most important step--with a marker (Sharpie works fine) mark the base of the distributer and a point on the block ,or somwhere, to align up with when you put the distributer back in--unplug the electrical connector in the back of the distributer (cam shaft sensor)...take a carefully loosen the distributer hold down bolt (13mm or 1/2 inch wrench) and remove the distributer. There will be oil dripping so be ready with a rag. Look carefully at the distributer gear. It is very common for these gears to to wear out. The replacement gear should be made of iron or hardened steel--these cost around $70. Check the price on a whole new distributer.
    To reinstall the distributer it is the reverse, but make sure the base is aligned with the (Sharpie mark). Sorry you are not done with the distributer reinstall--Now you must take the truck to the dealer to get it properly timed. The ignition timing on your engine MUST BE SET WITH A SCAN TOOL. It is almost impossible to reinstall the distributer back to the exact same spot--especialy if you replace the gear. Unfortuanatly the dealer is usually the only shop that has this type of scan tool.
    The timing may be the problem all along, because I am sure that after the distributer was removed by the mechanic, the engine timing was not set with a scan tool. This is a common oversight. Also if you replaced the crank shaft position sensor--and you are taking the truck to the dealer for a timing setting you mine-as-well have a crank shaft relearn proceedure done while it is there. The reason for this is too long to explain--just tell the dealer you want a the timming set and a crank shaft position sensor relearn proceedure done--it will take about an hour and will set you back around $60 bucks--A tip--before you bring the truck to the dealer make sure the engine is warmed up for at least 1/2 hour.....Also, I would get rid of the champion spark plugs and the duralast wires--why?--A/C Delco platinum plugs (not the rapid fire ones) and A/C Delco wires are the only brands that work on these engines--The ignition system voltage is very high--and for some reason A/C Delco is designed for this, trust me here. I know that A/C Delco plugs and wires are expencive but they are the only brand that works and they will last another 100000 miles..I would bite the bullet and put in new plugs and wires--see what happens...Keep me posted...
  • Thanks Pear69. I will work on the Burb again this Friday when I get off work. I will buy me the new set of A/C Delco Plugs and Wires. I will check everything you suggested and bring it to the dealer and have the crank shaft relearned and the timing adjusted. I will keep you posted. Thank you very much.
  • Hello Pear69. I live in California. I made an appointment to bring my truck in at the Chevy dealer and told them about my issue. They advised me about a special warranty for the sequential something and it will be check and repair at no charge. I don't know exactly what their saying but I'll bring the truck in.

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