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 Hesitation When Starting

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Zanethan



Posts : 9
Join date : 2014-11-15

PostSubject: Hesitation When Starting   Sat Jul 02, 2016 11:53 am

So my '92 TBI roadie has started hesitating when starting from a stop. It seems to bog down until the engine speed gets to about 1500 RPM then it takes off like normal and seems to be worse once the engine is warm. Once it's up and moving everything behaves normally. I have replaced all the spark plugs, the air filter, the fuel filter, and the fuel pump all of which made the engine run better but didn't resolve the issue. Additionally, I tested the TPS and it is behaving normally. The issue remains regardless of what gear I have the transmission in when starting (it does it in 1, 2, D, and OD) so I don't think it's the transmission (but I could be wrong) and it doesn't seem to ever slip. Any thoughts on what could be causing this? Engine has 187,xxx miles and runs fine with the exception of this.
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just me



Posts : 162
Join date : 2014-10-09
Location : Riverside, CA

PostSubject: Re: Hesitation When Starting   Sat Jul 02, 2016 6:16 pm

first free test would be to pull the vacuum hose off the EGR valve, plug it and see if the problem remains the same.
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Fred Kiehl

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Posts : 4867
Join date : 2009-11-13
Age : 69
Location : Largo, FL 33774

PostSubject: Re: Hesitation When Starting   Sat Jul 02, 2016 10:21 pm

Clean the ground at the thermostat housing. Do it when the engine is cold. Use a metal gun bore brush and some WD40 in the threaded hole. Wire brush the stud, and clean the lugs. The ground is for the computer and the O2 sensor (and maybe a couple more things). You might also check the coolant temp sensor for the computer (not the one for the gauge). Another check is the IAT sensor on the toaster.

You can check the CTS in a pan of water. Heat the water, while checking the resistance with a VOM. It should change in a linear fashion. The IAT can be checked with a hair dryer (cool to warm) for a similar reading. Your O2 sensor can be checked with a propane plumbing torch...similar reading. The O2 sensor is easy to remove, just do not touch the working part with your fingers, or get anything on it, and put anti-seize on the threads before reinstalling. I use a crescent wrench to remove mine. The connector is above the engine cradle.

You may have a small vacuum leak. The local parts store may lend vacuum testers (you pay for it, and get your money back when you return it...a credit card works great for this). The hoses and fittings get really brittle from age. You can make a new manifold from parts at your local parts store. The only part you may have trouble finding is the dual one for the EGR solenoid.

Check all of your wires for cracked insulation. The cars are 24 years old, and the insulation is getting brittle.

The last and worst option is that the wiring that runs under the front of the engine has been compromised. Over the last 24 years, the insulation has probably become one lump, and the wires may inadvertently touch. This is a last resort check, because it is a PITA, and would require rewiring everything that goes under the front of the engine. The O2 sensor, alternator control, and vapor recovery purge valve wires go there, among others.
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Fred Kiehl

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Posts : 4867
Join date : 2009-11-13
Age : 69
Location : Largo, FL 33774

PostSubject: Re: Hesitation When Starting   Sat Jul 02, 2016 11:30 pm

PS. check your PCV port in the TBI. If it is clogged, it can cause a lot of weird symptoms. The PCV valve must work properly as well.
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Zanethan



Posts : 9
Join date : 2014-11-15

PostSubject: Re: Hesitation When Starting   Sun Jul 24, 2016 11:56 am

So an update on this.  It is not the O2 sensor as I have replaced it and the issue still remains.  But I have discovered that the issue is dependent on the ambient air temperature.  If it is over 90 degrees out then the car hesitates almost every time but if it is below 90 then it doesn't do it as often and if it is below 80 it won't do it at all.  Seeing as its dependent on ambient air temperatures would that lend itself to being a faulty IAT?

Additionally, the SES light comes on if I am stopped long enough but will turn off again after driving about 2 miles. Might the IAT be getting saturated with heat as it sits triggering the code then once I start moving it cools off enough to turn off the light.
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Fred Kiehl

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Posts : 4867
Join date : 2009-11-13
Age : 69
Location : Largo, FL 33774

PostSubject: Re: Hesitation When Starting   Sun Jul 24, 2016 12:58 pm

You need to pull the code. It could be the CTS.
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Zanethan



Posts : 9
Join date : 2014-11-15

PostSubject: Re: Hesitation When Starting   Sun Jul 24, 2016 2:11 pm

I don't have a OBDI scanner, but I tested the resistance of the IAT and it checked out OK. Is the CTS in question the one next to the thermostat?
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Fred Kiehl

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Posts : 4867
Join date : 2009-11-13
Age : 69
Location : Largo, FL 33774

PostSubject: Re: Hesitation When Starting   Sun Jul 24, 2016 5:51 pm

You do not need a scanner. You can cross the A and B terminals of the ALDL connector under the dash, turn the ignition switch to on (without starting the car), and count the flashes of the SES light. You will get a 12, 12, 12 then the codes in sequences of three times each number. You can get a small tester at the local parts store for about $30, that will plug into the ALDL connector, if you can not figure out how to short the two pins.
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Zanethan



Posts : 9
Join date : 2014-11-15

PostSubject: Re: Hesitation When Starting   Thu Jul 28, 2016 9:19 pm

So I pulled the codes and I'm getting the following codes:

33- MAP sensor signal voltage was too high (low vacuum) for 5 seconds when throttle opening was under 4%

45- Oxygen sensor voltage was over 0.75 volts for 30 seconds with a throttle angle above 20%.

Previous to pulling the codes I found some of the small diameter emission tubing to be broken in two places. I patched the tubing using some vacuum hose and from a shortish test drive it seems to be better. Based on code 33 and the cracked emission tubing it looks like it was a vacuum leak.
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Fred Kiehl

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Posts : 4867
Join date : 2009-11-13
Age : 69
Location : Largo, FL 33774

PostSubject: Re: Hesitation When Starting   Fri Jul 29, 2016 7:29 am

The map sensor will now tell your computer to give you a different mixture, and the O2 sensor will then read a correct mixture so that should fix both codes. Make sure the codes are removed from the computer. There is a fuse on the relay bracket at the rear of the passenger's side of the engine compartment. Remove it for 60 seconds, and you will erase the computer memory.
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