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High engine revs

Tiny
ALLAN CHETTY
  • MEMBER
  • 1988 CHEVROLET CAMARO
  • 0.5L
  • V8
  • 2WD
  • AUTOMATIC
  • 100,000 MILES
The car starts and idles smoothly, idles between 1,500 and 2,000 rpm's very slight dip in idle seldom. It also changes to overdrive excellence, no slipping. The issue is at 100 kmp the revs do not drop to around 2,000 and 3,000 rpm's like it used to. I ran like that about 500 km.I dropped the transmission undercover and my word the filter was black but the oil was still reddish and no smell. Incidentally I put a new transmission shifter cable and used to battle to get it out of park but other gears changed fine. The cable I used was bought from a v8 shop in South Africa and was twice the size of original but we made it work. I retired the engine. Checked for damaged hoses all good, took out IAC valve and cleaned it out, changed MAP sensor, that's were I am. Today I want to take out EGR valve and clean, when I play with the temperature sensor that controls idle on top before the TBI there is a fluctuations, but when the engine warms up the idle drops so I presume that's working, any further inputs thanks guys God bless you all for your time and services. Regards Allan Chetty
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Thursday, March 26th, 2020 AT 11:15 PM

28 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
We need to run through these guides and see what turns up. We may find the solution or at least alter the issue to point to the issue.

https://www.2carpros.com/articles/engine-idles-too-high

I suspect there is a possible vacuum leak that is pumping up the RPM.

https://www.2carpros.com/articles/engine-idles-too-high

You have already done some of these things but let me know what happens. Also, the EGR is not a bad idea so again, update us after you review this material and inspect/clean the EGR. Thanks
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Saturday, March 28th, 2020 AT 8:43 AM
Tiny
ALLAN CHETTY
  • MEMBER
  • 31 POSTS
Thanks for response. The rotor was cracked which I glued and car started rite up (we are on lock down cannot purchase parts), my OBD is not showing any faults, the idle still revs at bet -15/20k rpm's. The only other thing could be TPS or IAC valves which I don't know how to test. But when unplugged the EGR engine cuts out, when TPS or IAC unplugged car does not falter.
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Sunday, April 5th, 2020 AT 4:04 AM
Tiny
KASEKENNY
  • MECHANIC
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I attached how to replace the IAC assuming you have an electronic fuel delivery system (injectors not a carburetor). It could be the IAC but that normally causes an erratic idle or stall at idle.

If you have high RPM we need to check for a vacuum leak. Here is a guide that runs through this:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

I also attached the fast idle adjustment. Again, if you have a fuel injection system then you don't have a way of adjusting idle speed. However, if it is high then we need to run through this info and go from there. There is a chance that it is a throttle sensor but that would normally have a fault code so let's start with this info and go from there. Thanks
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Sunday, April 5th, 2020 AT 8:14 AM
Tiny
ALLAN CHETTY
  • MEMBER
  • 31 POSTS
Thanks. Will run through. Stay blessed.
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Tuesday, April 7th, 2020 AT 12:48 AM
Tiny
KASEKENNY
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Thank you. You as well. Let us know how it turns out. Thanks
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Tuesday, April 7th, 2020 AT 8:50 AM
Tiny
ALLAN CHETTY
  • MEMBER
  • 31 POSTS
Hi, tested the IAC and it moves so that works. I went back to checking timing and upon revving the engine the timing mark retards left way out the mark plate. I got the timing set at 6% btc. It idles with a dip randomly.
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Wednesday, April 8th, 2020 AT 6:56 AM
Tiny
ALLAN CHETTY
  • MEMBER
  • 31 POSTS
Hi, just a thought. The car starts on the button just perhaps the timing could have jumped a tooth after interfering with the timing it's now backfiring and very rough. Also loss of power. Plugs are new, the wires recently replaced.
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Wednesday, April 8th, 2020 AT 9:50 AM
Tiny
KASEKENNY
  • MECHANIC
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You have a timing chain and that is unlikely to jump timing but based on what it is now doing especially the backfiring, we need to check it. I attached the timing marks and chain replacement process. I don't think you need to replace it unless you find it is off. If it is, the chain could be stretched and need to be replaced.
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Wednesday, April 8th, 2020 AT 6:04 PM
Tiny
ALLAN CHETTY
  • MEMBER
  • 31 POSTS
Thanks. God Bless.
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Wednesday, April 8th, 2020 AT 11:11 PM
Tiny
KASEKENNY
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You are welcome. You as well. Thanks
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Thursday, April 9th, 2020 AT 12:09 PM
Tiny
ALLAN CHETTY
  • MEMBER
  • 31 POSTS
Good morning friend this is a historical day for us. May you and family continue in His blessing. Car question. By gluing the cracked rotor do you think the sparks jumping all around and causing the backfire and erratic idle? Ta
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Thursday, April 9th, 2020 AT 11:02 PM
Tiny
KASEKENNY
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That it is. Thanks. You too.

It depends on where it is cracked. If it is just the plastic portion then it is okay. However, if it is near the metal tab then it could cause the spark to jump to another ground source. Basically this electrode is allowing the spark to leave at the tip as it searches for ground. If it finds an easier path then it will take it. However, this normally causes a misfire and not necessarily a backfire. However, anything is possible if the spark is erratic. If it is just the rotor I would replace it because they are normally pretty cheap.
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Friday, April 10th, 2020 AT 7:10 PM
Tiny
ALLAN CHETTY
  • MEMBER
  • 31 POSTS
Thanks Kenny, I watched the injectors the spraying of fuel, when cold car idles 3,000 rpm's, no miss, when a little hot idle drops to 2,000 rpm's then occasionally I see extra fuel like drops in a second and causes the surge, is there any way to test the ECM? Also the oxygen sensor has never been changed. Thanks, stay blessed.
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Saturday, April 11th, 2020 AT 1:23 AM
Tiny
KASEKENNY
  • MECHANIC
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Okay. You mentioned it earlier but you have the Throttle Bore Injection (TBI) system, correct? If you did, where did you see the fuel drops? Were they coming from the injector? If this is the case, I don't think you have an ECM issue. I suspect you have a leaking injector or possible just a "dirty" injectors that is causing fuel to drip from it.

However, if you have seen this and that is when the surge happens then you found the issue. Clearly more fuel is going to raise RPM so we need to suspect an injector issue. The injectors are only supposed to deliver fuel when they are opened (pulsed) by the ECM and it is only supposed to spray fuel, not drip fuel. So if it is dripping fuel then that is either it remaining slightly open or there are deposits in the nozzle causing fuel to drip into the the intake.

Take a look at this info and let me know what you think.
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Saturday, April 11th, 2020 AT 7:50 AM
Tiny
ALLAN CHETTY
  • MEMBER
  • 31 POSTS
Thanks Kenny, it's spraying like funnel constantly on idle, but occasionally just for a second it sprays extra then normal and both injectors spraying evenly not dripping. I'm stumped. Thanks for your time to respond, stay blessed.
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Sunday, April 12th, 2020 AT 2:49 AM
Tiny
KASEKENNY
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If both injectors are doing it evenly and they are normal spray patterns but just longer and that is causing the surge then that tells us that something is telling the ECM to open the injectors for a longer period of time. This means something is telling the ECM to do it or the ECM is faulty.

I know you said you checked hoses for damage but have you actually inspected for a vacuum leak? This will cause a random addition of fuel when the ECM sees a slightly lean condition due to the addition of the unmetered air.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge
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Sunday, April 12th, 2020 AT 1:44 PM
Tiny
ALLAN CHETTY
  • MEMBER
  • 31 POSTS
Hi kasekenny, trust all is well. We are in South Africa not too good (lock down stressful), but God is always in control. Car question the car at timed at 6$ before TDC and idles smooth at 2500/3000 at warmed idles 15/20k. The following I done: had distributor and coil tested at a test center, new TSP, checked all hoses, IAC I took out and upon key on it came out fully (working), all plugs and leads working properly. Took out TBI cleaned and that sprays evenly and fuel filter changed (was not dirty), obd no codes except 12. Revs no hesitation or backfire, but the moment put in drive stars to miss behave slight backfire, rough engine rocks. I am now stumped.I even tried to move the TPS position slightly -no difference. The plug into TPS was broken and I don't know if I pined that right. I got the blue on top and bottom left black and white on bottom right. I tested the ref, on blue wire reads below 04 ohms. Any help is welcome. God Bless.
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Sunday, April 26th, 2020 AT 1:49 AM
Tiny
KASEKENNY
  • MECHANIC
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It's great that you always start your posts with the real priority.

As for your high idle, as you are aware with it being TBI, idle speed is not adjustable. However, there is one process that we can try to reset which is the minimum air rate which will hopefully relearn the ECM's ability to control the idle.

I attached the process. Also, at idle we should be around 500 RPM and there is a chart showing the TPS voltage. When the vehicle is idling, note the RPM and then measure the voltage of the TPS. If the TPS is correct voltage but still has high idle then we know it is not the TPS.

Let me know what you find. Thanks
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Monday, April 27th, 2020 AT 7:30 AM
Tiny
ALLAN CHETTY
  • MEMBER
  • 31 POSTS
Hi Kasekenny, trust all is well on your side. We in South Africa still on lock down, and the virus not flattening, but by His Grace he will see us through.I found that there was a break in TSP connector and fixed that, also the color wire to pin connection was not roght as the original pliu in is broken. It seemed a little better, I also reset the IAC as per your guide; the car seemed much better but still not smooth when in gear. The idle seems around 20k and comes down to 15 rpms and fluctuates there, the pintle came off and I screwed it back and I think that is now my major issue as to how much to screw in. I closed loop the engine but still its rough in gear, but idles constant with no hesitation but dips below 20 rpm's to 15 and back up again, the engine itself is not shaking, and my timing set at 6 degrees before TDC. Thank you for taking the time to walk me through. God Bless you and family.
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Wednesday, April 29th, 2020 AT 3:42 AM
Tiny
KASEKENNY
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It will get better.

You mentioned it a number of times but I never checked it. The timing on this engine appears to be 0 BTDC. Lets set the timing there and then see what happens. 6 degrees shouldn't make that much of a difference but it could. Worth a try.
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Wednesday, April 29th, 2020 AT 6:32 PM

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