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Old 04-02-2012, 10:54 PM   #1
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Hot Start Rough Idle

So ive been having this problem with my Camaro. Its a 305 tbi. It starts fine when its cold or has sat a few hours after driving, but if i try to start it 10 min or longer after driving the idle is very rough. It fluctuates rpms drastically and sometimes even cuts out. If i rapidly press on the gas pedal until the rpms get up then floor it, it usually gets past this and then it idles and drives fine. Once in a while when driving when i go to give it gas, its really sluggish the rpms drop but once it gets through it it will run fine. Ive already replaced the MAP relay, TPS, ICM, FP relay, cleaned the IAC and TB and injectors, Replaced the coolant temp sensor, theres no vacuum leaks that Im aware of we went over the whole system. We took it to the local parts store to see if there were any codes and came back with nothing. The check engine light comes on while driving but shuts off as soon as i shut the car off, only comes on while driving. Was wondering if it could possibly be the oxygen sensor or maybe the EGR valve? If not maybe something else? Hopefully nothing to serious. Also one of the previous owners spliced in a thin wire (did a terrible job at that) into the orange wire that runs to the ECM/FP fuse by the battery, it runs all the way to the door jam on the passenger side behind the dash...could this maybe be the cause? I havent traced it yet but will as soon as i can. Any help is appreciated!
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Old 04-03-2012, 07:50 AM   #2
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Re: Hot Start Rough Idle

Anyone? Any help appreciated as this is my daily driver and need to get her running good again!
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Old 04-03-2012, 01:11 PM   #3
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Re: Hot Start Rough Idle

Also I traced that wire and its connected to the constant 12v wire on the radio...this shouldn't be causing my problem right?
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Old 04-03-2012, 01:20 PM   #4
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Re: Hot Start Rough Idle

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Also I traced that wire and its connected to the constant 12v wire on the radio...this shouldn't be causing my problem right?
even if it isn't it should be fixed.

if your check engine light is on you can and should pull codes. if you cant pull codes your likely dealing with a bad ECM.

http://www.freeautomechanic.com/diag...blecodes5.html

how to pull codes by your self. read up.
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Old 04-03-2012, 01:33 PM   #5
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Re: Hot Start Rough Idle

It only comes on while driving though. I can sit usually all day parked or take it around the block and it usually doesn't come on. I go drive for 15 min it comes on. Shut the car off turn it back on its gone. Should be noted that I have a smog delete. My rough idle was occurring before we removed the smog to. And about the wire, if I disconnect the constant will the radio still work? Because I want to remove that wire that's spliced in to see if it helps but is connected to radio as I stated before.
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Old 04-03-2012, 03:18 PM   #6
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Re: Hot Start Rough Idle

the constant 12 volts should be run from the orig. radio fuse in the fuseblock.

if your CEL / SES comes on at all, a diagnostic trouble code is recorded for later retrieval. read the instructions @ the link i provided and post the results. its the easiest step in diagnosing an engine performance issue.
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Old 04-03-2012, 08:20 PM   #7
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Re: Hot Start Rough Idle

Okay well ill have to go back and rewire that..as for the codes i did what the link said and came back with code 23 = MAT and code 32 = EGR. Where should i start on both of these or things to check first? Also location would be very helpful to. I believe MAT is in air cleaner? and EGR is...? If anyone has pics that would be great to! Thanks for your help so far z28romance its much appreciated!
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Old 04-04-2012, 07:24 AM   #8
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Re: Hot Start Rough Idle

No problem with the help. unfortunately im not very familiar with TBI. what i can tell you is the best thing you can do for yourself is at the very least get a hanes manual for your car.

not sure where your egr is. maybe someone can chime in here or you can do a google search.
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Old 04-04-2012, 05:46 PM   #9
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Re: Hot Start Rough Idle

So i fixed the wire, thats all good now.
As for the starting issue i know where the EGR is located but where is the MAT sensor located?? Is it in the air cleaner or manifold or possibly somewhere else? Does my car even have MAT or is it something else? I keep getting different placements for it and different types of sensors everytime i try to search for it. And if its in the air cleaner the one they sell at autozone doesnt look anything like it! Also the EGR gets its readings from the MAT am i correct? So i want to fix that first. Im just a little confused with this right now.
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Old 04-04-2012, 09:19 PM   #10
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Re: Hot Start Rough Idle

Well just a couple hours ago i bought a new MAT sensor, it goes in the air cleaner. (some places call it an air charge system) I reset the ECM, drove it around, and its not throwing code 23 anymore. Still throws code 32 for EGR. If anyone knows anything about this please help! My issue is still occuring! I was also thinking maybe oxygen sensor? I heard it doesnt always throw a code when they go bad...PLEASE HELP!!!
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Old 04-05-2012, 09:23 AM   #11
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Re: Hot Start Rough Idle

if you know where your EGR is check and see if its in good condition. i know the ones on the TPI cars you can move the diaphragm by hand and see if the valve is moving freely.
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Old 04-05-2012, 09:31 AM   #12
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Re: Hot Start Rough Idle

Yea i know where its at now. I get out of class soon so ill check before i go to work. Those are supposed to be closed when throttle isnt open and then open up when throttle opens, am i correct? Thanks again!
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Old 04-05-2012, 10:38 AM   #13
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Re: Hot Start Rough Idle

Ok so I just checked out the diaphragm and I think its not working right. Its all the way down (towards the engine) and I can move it with a screw driver when I push on it, not with to much force, but when I go to accelerate it just kind of wobbles but doesn't open (move away from engine) I have vacuum to it I checked the hose while I held the accelerator and there was suction. Does this mean the valve is bad? That is what I'm thinking now sense it doesn't really move "freely"
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Old 04-05-2012, 04:13 PM   #14
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Re: Hot Start Rough Idle

if its original then its a good idea to replace it anyways. if you have a vac pump you could see if its moving by applying vacuum to it. the problem might lie in the circuit itself. check the wires to the solenoid. test the solenoid itself.
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Old 04-05-2012, 05:23 PM   #15
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Re: Hot Start Rough Idle

The EGR valve is opened by an ECM controlled solenoid. The solenoid is fed by ported vacuum. The solenoid prevents the valve from opening when the engine is cold, then the ported vacuum only opens the valve at part throttle when manifold vacuum is high(manifold vacuum drops under load or when accelerating). The valve should be closed at idle. As far as testing the EGR with a vacuum pump, be aware that many EGR valves are pressure modulated. This means that they only open when there is sufficient exhaust pressure. These valves may not open very well with vacuum alone.

On the other hand, most any vacuum operated EGR valve should at least open slightly when the throttle is snapped. Be sure when checking though that that the EGR solenoid is turned off(these systems energize the solenoid to disable the EGR valve). You can simply unplug the solenoid, or wait til the engine warms up to test the valve.

As far as your rough idle when warm. The EGR valve would only cause this if it's stuck partly open, allowing exhaust gases into the intake air stream. A closed EGR will not affect drivability excepet that it causes higher than normal combustion temperatures which can lead to detonation on a hot motor. To be sure that your EGR valve isn't sticking open, you may want to remove it and clean the carbon out if. Be sure that the spring in the valve is in good condition and that the valve snaps closed solidly.

Other possible causes of your hot start issue are a leaking injector flooding the engine with fuel after the engine is shut off. The o-rings that seal the injector to the TB are very easy to screw up when swapping injectors. Look down the throttle bore as the engine is shut off. Can you see any dripping fuel?
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Old 04-05-2012, 08:26 PM   #16
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Re: Hot Start Rough Idle

Well I went ahead and replaced the EGR valve cause it was old and didn't seem like it was working right, I WA also getting code 32. After replacing there isn't a code 32...now for the rough idle I just got home and had my brother shut off the car while I watched the injectors, I didn't see any dripping or leaking...this has me stumped and ethos is my daily diver so it would be nice to get her normal again. anything else I should check?
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Old 04-05-2012, 09:12 PM   #17
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Re: Hot Start Rough Idle

I would be very suspicious of a leaking TBI setup. I'd put a paper towel or something under the injectors after it's shut off and watch REAL close for a little while. The symptoms really seem to match up pretty well with it flooding.
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Old 04-05-2012, 09:42 PM   #18
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Re: Hot Start Rough Idle

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I would be very suspicious of a leaking TBI setup. I'd put a paper towel or something under the injectors after it's shut off and watch REAL close for a little while. The symptoms really seem to match up pretty well with it flooding.
Thats exactly what we just did today, about an hour ago. There was no leaking/dripping, nothing...now i just noticed this while driving, under WOT it seems like there is no power. (i dont beat on my car but figured id test everything out today) im better off pushing down halfway on the gas and it goes faster/more power. Now the engine seems like its working hard but either a. theres something wrong with the tranny or b. its not getting enough fuel. Now i was thinking fuel pump but that seems to be working fine. Would a bad fuel filter or fuel line possibly cause all these problems im having? If not its back to square one and im going to look at the plugs and wires and the distributor and coil.
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Old 04-05-2012, 10:56 PM   #19
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Re: Hot Start Rough Idle

Fuel pump sounds possible. If that's what it is please dont cut a hole in the back of the car to get to it.
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Old 04-06-2012, 12:45 AM   #20
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Re: Hot Start Rough Idle

Well i know for fact its not a clogged cat, mines already gutted because we had problems with it a couple months ago. I dont think its fuel pump because we can hear it and see the injectors spray when it turns over. So eliminating those my question is could a bad fuel filter or fuel line (i read somewhere in the forums about the fuel lines) cause a rough idle and surging??? or would that only affect the driveability??? Thanks for the input and help guys! My dads bent on the fact it has something to do with spark or ignition. I think its fuel related. Like i said before no codes anymore thank god! and thanks for the help with that z28romance!
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Old 04-06-2012, 07:27 AM   #21
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Re: Hot Start Rough Idle

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Well i know for fact its not a clogged cat, mines already gutted because we had problems with it a couple months ago. I dont think its fuel pump because we can hear it and see the injectors spray when it turns over. So eliminating those my question is could a bad fuel filter or fuel line (i read somewhere in the forums about the fuel lines) cause a rough idle and surging??? or would that only affect the driveability??? Thanks for the input and help guys! My dads bent on the fact it has something to do with spark or ignition. I think its fuel related. Like i said before no codes anymore thank god! and thanks for the help with that z28romance!
no problem at all 91'CamRS. just make sure you keep her alive. i wish i knew more about tbi setups.
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Old 04-06-2012, 07:29 AM   #22
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Re: Hot Start Rough Idle

have you had your distributor opened up 91'CamRS? i know on my TPI the injector pulses are modulated by the pick up coil. mine had some corrosion and was causing nearly the same issue.
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Old 04-06-2012, 11:39 AM   #23
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Re: Hot Start Rough Idle

The HEI distributor could very well be suffering a heat related failure. Odd though that the engine runs fine til it's shut down, and that the rough idle is only right after a hot start. Since we've now verified no leak at the injectors, I would like to see what fuel pressure is doing. He may have a tank pressure issue or a leaky purge valve that's causing him problems. To eliminate the purge valve as a cause, simply disconnect and plug the hose from the purge valve to the throttle body. To eliminate a tank pressure issue, you should be able to disconnect the vapor line from the canister to the tank and any tank pressure will be relieved.
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Old 04-15-2012, 03:56 PM   #24
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Re: Hot Start Rough Idle

I would like to think its something electrical now. I have pressure in my tank, every time I take the gas cap off there's some pressure built up. I put a timing light/spark light (don't know what its called on the other day when it was hot, started the car and when it wants to stall it almost is like its not getting spark and the light blinks slow. Then it goes back to normal until it wants to surge again. I was thinking maybe plugs or coil. Also a new problem occurred today. Went to start the car when cold, sat over night, and it idled really high...was thinking iac. How do you test that?
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Old 04-18-2012, 07:07 PM   #25
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Re: Hot Start Rough Idle

Pressure in the tank is normal up to about 14"H20. That's about 1/2 PSI, which doesn't seem like much but as you open the gas cap and have this pressure release at you it seems like alot. I started out thinking you may have a distributor problem, based on your initial description of the problem. Now I'm beginning to think you may have an injector issue. This could certainly the hard start hot. It would also explain your uneven idle. The best way really to check injectors is to remove them and send them in to be tested on an injector bench. On the bench they will be ohm tested cold and hot, the nozzles will be checked for clogging, and any sticking pintles will be uncovered. The injector shop will clean them, replace them as needed for a good price, and send you back a flow balanced set.

As far as the flashing of the timing light strobe goes, it's normal for it to flash slow at low idle speed. It flashes with each firing of the cylinder you have it on. Each cylinder fires every other revolution of the crankshaft on a four stroke engine.
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