Wow, I can't finish fixing one thing before I have another problem anymore!!!

Here are my symptoms:
- Idles OK - maybe just a tiny rough
- While just driving or accelerating lightly it hesitates and surges. This feels and sounds like my car is about to die right there.
- If you give it a lot of gas it smoothes out and goes.

I recently replaced the plugs/wires/cap/rotor/air-filter/pcv and before that I swapped the intake manifold gasket. I'm not sure if the problem pre-existed the tune-up. I know I did the tune-up for a reason, but these symptoms are worse than before that's for sure.

Any ideas on where I should begin? I can't even guess as to whether its fuel/ignition/vacuum!

My car is beating me to a pulp lately!




Thanks for any and all suggestions!

 

When you put everything back together (manifold, TB, plenum, & runners) did you use a torque wrench or the old calibrated wrist method to tighten the bolts. Check for vacuum leaks. Are you getting a check engine light.

 

Might have an internal vacuum leak (from the intake manifold).

Make sure your timing is on and that you didn't fry a plug wiring. Easy to do, even though they are new.

 

Hi Trickster!

Hah! I definitely used a real torque wrench and not my calibrated wrist on the intake stuff!

Its the first time I ripped apart a TPI, but I felt pretty confident that all the gaskets were arranged properly and that its tight.
Anyhow, should I re-torque or somehow check for leaks there?

- No codes.

- Verified my timing 6* BTDC.

- Timing is advancing with acceleration.

- Vacuum about 17" at idle.

Throttle Manipulation:
When I turn the throttle assembly just a tiny bit from the idle stop. The engine speeds up and the vacuum goes up to maybe 17.5".

When I turn it a just bit more the engine starts to bog. If I turn it just a bit more than that and it starts really bogging and sort of loping (speeding up and slowing down). At that point my vacuum is down at about 10".

Now, if I turn it a bit more than that it starts speeding up - smoothing out - and vacuum goes up again maybe to the 15" range.

TPS:
I checked my TPS (I still have my service manual at my friends house from my last job). Anyhow, I checked the resistance of the TPS with a multimeter and had 7.5K to 3K or so for the full range throw and it seemed to travel smoothly. It never went backwards in resistance from what I would have expected. So, I don't think its completely out of whack.

Vacuum Leak Check:
I sprayed water from a spray bottle and covered everything hoping it would help me find some of vacuum leak. It did nothing except make my engine wet. I'm not even sure what I would see if it did get sprayed on a leak. I do have some questionable hoses in there, but they seem to be holding.


I just read something in the Haynes diagnosis about fouled plugs from repeated short trips. Well, I've been working on my rear-axle and some other things. Just prior to this I used the hose clamp method to try to improve my driveshaft balance. Well, I must have started and shut down the engine 50 times doing this. Add maybe 50 starts from the previous weekend too. Maybe I fouled my plugs??? I'm going to check this next chance I get.

Seems odd that a fouled plug would work ok at idle and hard accel but not at slight accel??? I'm thinking this is something different and something that may have been around for a while but is worse now.

 

Twighlight:
Are you saying I could have a leak at the new intake manifold gasket??? I hope not!

I'll re-re-re-check my wires again!


EGR:
I just read something about EGR Valves causing symptoms like mine. Should I get a code for that?

 

That's what he is saying and also why I asked about using the torque wrench. If you were having a problem with the EGR, it would throw a code 32 at you. Have you also looked at the MAF connections. BTW, I don't know about the OHM resistance of the TPS, but I do know that the voltage range at idle is between .48 to .62 volts and 4.5 volts at WOT.

 

When I changed my plugs, after the intake manifold gasket, I did a pressure test. I got about 185lbs peak pretty consistently across all the cylinders. For 4 puffs, I got 165-170lbs.

I also had a cooling system issue after the intake manifold (broken heater control valve). After I fixed that I did a cooling system pressure test and that was fine too.

These, I think would rule out at least a couple potential internal vacuum leaks?

 

How could I check for an internal vacuum leak?

When I did the intake manifold, the hard lines going to the EGR crumbled. I bought some replacement hard lines and inserted them into the EGR solenoid rubber junction. I'm wondering if that could be causing a problem. The EGR Solenoid would think it was working but the EGR might not be activating. Anyhow, I'm streching it a bit. I'll have to do some more diagnostics.

 

EGR:
- Without the vacuum source to the EGR, engine runs smooth from 1K RPM to 2K RPM.
- With the vacuum source connected it bogs and stutters.

OK, so what is going on.... My EGR must be working but its being activated when it shouldn't be?


CTS:
CTS Resistance 825 Ohms - engine hot to touch but could hold. Chart says 130 degrees. I can believe it.

Fuel Pressure:
I energized the fuel pump for 3 seconds and popped my key into the schrader. The spurt went up about 18 inches. Seemed like a good amount of pressure. Wish I had a guage.

I wanted to step through the EGR SYSTEM DIAGNOSIS chart, but I can't get at the valve to do the first step!

 

To check for the internal vacuum leak, spray starter fluid around the intake while running. If the idle speeds up, or changes for that matter, you've got a leak.

Pull the PCV up, plug it with your thumb, and spray the starting fluid in the valve cover, again engine speed changes, leak on the inside.

Sometimes you just can't proove you have an internal leak, you just have to change it as that may be the last thing.

When my plugs were fouled, it would idle a hair rough, and studder under partial accel... but wide open would be okay. Spark is very load sensative. If you replace the plugs and nothing changes, it's an easy $10 check. New plugs are always a good thing anyhow.

Change those before changing the intake gasket unless the tests proove you have a leak!

 

Hmmmm the old '18 Inch Spurt Test'........
I can't find that procedure in the books...

Get a gen-u-wine fuel pressure gauge on there.
Look for about 40 PSI at idle.

Remove the plugs and inspect the insulators with a magnifying glass. Sounds like you could have cracked one either taking them out or putting them back in.
This causes a hard to find skip/miss/random misfire/run good/run bad symptom.

The TPS 'could' have a bad spot in it just off idle.
This would drive the ECM nutz and it would respond by jacking the injector PW's all over hecks creation.
It 'should' throw a code but it's not 'written' that it HAS to.

Change the TPS, they are only about 7 bux so changing it as a diagnostic measure is not out of the question.

Good luck with it.

 

VetNutJim:
Yes, I found that test somewhere on these boards! :-) Well, they didn't characterize it in inches though. I added that part to make it more scientific! I've now gone to 3 parts stores and each of them was out of the fuel pressure tester that goes in my range. I at least want to see one! Any recommendations?

I finally picked up some starter fluid. I'm actually looking forward to getting to try that. It seems like it would work good. I'm still sort of afraid of that stuff though.

Lots of tests to do and no time during the work week or car is way too hot!

I'm now driving with my EGR vacuum line disconnected. It seems to help a lot. It gives me enough confidence that I'm not in a panic anymore. Its actually running OK. I also have not thrown any codes yet even w/ the EGR competely disconnected. My drive to work is about an hour and I've made two trips already like this.

Listen to this and see if this sounds right to you guys. I hooked up a vacuum guage to the line coming from the EGR Solenoid that would normally go to the EGR. I'm seeing the following:

RPM - Vacuum
---------------------
1000 - 0
1100 - 0
1200 - 10" (Quick step up right at 1200)
1700 - 15" (smooth transition up to 2200)
2200 - 17" (full vacuum)
2300 - 17" (stays at full vacuum above)

Guess what, whe the EGR is connected I start to have trouble with the idle right at 1200 getting really bad at 1700 then clearing up at around 2000 RPM.

I don't believe my solenoid should be kicking in at all until over 2000 RPM.

With EGR connected, I have lots of trouble idling smoothly between 1200-2000 RPM. With the EGR disconnected its smooth right through.

I'm a little nervous to be running w/o it because I know my timing will be too advanced like this.

 

Have you changed your EGR at all? Just trying to eliminate the possibility you got a Pos and not a Neg. or vica versa.

 

I've never changed it.

 

its probably the egr valve mine was stuck completly....and code came up only on highway...but would never stay and it was just rich/lean bad injectors i just found out :-( anway also check your
o2 sensor easy check since leave egr connected....dissconnect the wire for the o2sensor and drive if it runs better replace o2...if not than its osmething else how ever the o2 is supposed to be replaced ever 25,000 miles the one on the manifold....spend the few dollars for a socket too o2 socket and check around at places that its got the clip installed and you can get it for $20 dont buy the 80dollar one its the exact same sincle wire


just replace the egr valve buy it from kragen and buy the standard because standard buys from oem GM (rochester) so you get the best part for the car but the cheapest price too. also check to see which egr valve you have there are 3 types positive negative and universal. on the egr valve itself is the numbers at the very end of it is a p or n or no letter make sure you buy the right one. also check your maf....

 

I'm having the same trouble, except I sometimes get an SES and my car has been dying at stops randomly....

 

I had this same problem when i did my TBI/TPI swap. The problem was solved when I disabled the highway mode in the chip. For some reason the highway mode is really really stingy when it comes to fuel and causes stumbling. The engine now runs smooth at part throttle.

 

Found the problem..... Its my EGR Vacuum Solenoid.

Well, I had noticed that my vacuum to the EGR was present even when the engine was cold. That led me to investigate further.

Suddenly, I came to the realization that the vacuum being supplied to the EGR solenoid was ported. That means at idle the vacuum will be just about zero and will go up as I documented previously.

I did some more testing on the EGR solenoid it is passing vacuum to the engine 100% of the time (if its there). I pulled the solenoid and its an open circuit.

I re-adjusted my TPS to 0.54V. Then I set my IAC - well I should have pulled the EST cable first because it caused me to adjust down 150RPM, but when I finally pulled the EST the RPMs dropped 150 so I had to adjust it back up. I never had to punch out my idle adjust screw hole since it ended up getting adjust back up to where it was. I know because I didn't have to readjust my TPS.

The reason I checked the resistance on the TPS was just to verify that it incremented smoothly and didn't go backwards which would mean it would mess up the ECM as VetNutJim pointed out.

I'll have to order the EGR Solenoid, they don't have them in stock anywhere around.

So, Trickster and Twilightoptics were correct... Internal Vacuum Leak, but it was through my EGR.

I'm still going to do the vacuum leak testing when I get the solenoid and can spend some more time.

 

So, the real question is.... Why aren't I setting any EGR codes???

My EGR Solenoid is now removed and the EGR is never being activated? But STILL no codes. It has a temp sensor that I would think would detect that its not activating. I drive 1 hour to work each way on the highway (70MPH+). I even ran it in 4th to get my RPMs up for a long strech. I know the temp sensor isn't stuck because the CPU would detect that - I think - when the engine was cold.

I'm still confused on that one...

The solenoid only has 2 connectors, so it doensn't have the ability to check itself as I believe some others do. So, it makes sense that the ECM wasn't noticing the bad solenoid.

Anyhow, I'm happy for now.