"I've heard that the car will run fine without EGR, and that performance may actually improve. Is this true?"
Yes, you can disconnect them and plug the vacuum line, but my thoughts are to leave them alone - disconnecting them DOES NOT appreciably improve performance. Removal can cause "ping" when the engine is hot and affect gas mileage. They only work at high port vacuum and high temperature anyway. Their purpose is to cool (strange - hot exhaust cools?) the combustion gases, lower temperature, reduce detonation and reduce HC (NOX?) emissions. Some performance theorists believe that by disconnecting the EGR the air/fuel mixture is always higher in oxygen, giving faster re-acceleration after backing off on the throttle. I've tried it with and without. I choose to leave mine connected.
From: Randy T. Agee
The ECM DOES NOT control the 2.5's EGR valve, or know they are there - except for the O2 content in the exhaust.
From: Randy T. Agee
A short while ago there was a lot of discussion about how the V6 EGR system works. This post should answer any questions. I'll start with the tables used to determine how much EGR there should be under various operating conditions. The tables are indexed by the current engine RPM and intake vacuum. Indices outside the range of the tables are pinned to the range. Indices that fall between two rows (or columns) interpolate between those rows (or columns).
This table is used for all 4-speed and 5-speed models:
: 0 2 5 8 10 12 15 17 20 30 40 50 KPa vacuum
.......................................................
600 RPM : 0 0 0 0 0 0 0 0 0 0 0 0
800 : 0 0 0 0 0 0 0 0 0 0 0 0
1000 : 0 0 0 0 30 30 40 50 50 50 50 30
1200 : 0 0 0 0 30 30 40 50 50 50 50 30
1600 : 0 0 0 0 30 30 40 50 50 50 50 30
2000 : 0 0 0 0 30 30 40 60 60 60 50 40
2400 : 0 0 0 0 0 0 0 0 20 60 50 40
This table is used for most automatics:
: 0 2 5 8 10 12 15 17 20 30 40 50 KPa vacuum
.......................................................
600 RPM : 0 0 0 0 0 0 0 0 0 0 0 0
800 : 0 0 0 0 0 0 0 0 0 0 0 0
1000 : 0 0 0 0 0 0 0 40 60 100 70 30
1200 : 0 0 0 0 0 0 0 40 60 100 70 30
1600 : 0 0 0 0 0 0 0 40 60 100 70 30
2000 : 0 0 0 0 0 0 0 40 60 100 100 80
2400 : 0 0 0 0 0 0 0 40 60 100 100 80
This table is used for California emissions 3.33 ratio automatics:
: 0 2 5 8 10 12 15 17 20 30 40 50 KPa vacuum
.......................................................
600 RPM : 0 0 0 0 0 0 0 0 0 0 0 0
800 : 0 0 0 0 0 0 0 0 0 0 0 0
1000 : 0 0 0 0 0 0 0 40 60 100 70 30
1200 : 0 0 0 0 0 16 30 40 60 100 70 30
1600 : 0 0 0 0 0 16 30 40 60 100 70 30
2000 : 0 0 0 0 0 16 30 40 60 100 89 72
2400 : 0 0 0 0 0 16 30 40 60 100 100 80
The numbers in these tables correspond to the quantity of exhaust to include in each intake stroke. I do not know the conversion factor to convert the numbers into cc's. For those not versed in the metric system, 100 KPa is about the atmospheric pressure at sea level. So, by looking at these tables, it can be seen that even at a fast idle, there is some EGR. You should also notice that EGR is shut off at Wide Open Throttle. The current quantity of EGR affects two other ECM functions:
Ignition timing is advanced by a small amount given by the following table. This advance is not included if the ECM is currently lighting the SES light due to a code 32 (EGR feedback problem.)
: 0 16 32 48 64 80 96 112 EGR quantity (from above)
..................................................
most cars : 0.0 1.8 3.2 4.2 6.0 7.0 8.8 9.5 degrees
Cal 3.33 : 0.0 0.0 0.0 1.1 2.1 3.9 4.9 7.0
The fuel injector pulse width is reduced (enleaned) slightly as given by the following table. Note that the EGR flow will register on the MAP sensor - which will cause an increase in fuel delivery partially offsetting the reduction due to this table.
0 16 32 48 64 80 96 112 EGR quantity (from above) ............................... 100 98 97 96 94 92 91 90 %
So, what happens when you block off the EGR? First, the ECM will include extra timing advance (as much as about 6 degrees depending on the situation) that shouldn't be there. This might cause knocking - from the shape of the large table(s), this is most likely at moderate acceleration.
Second, the ECM will enlean the engine by as much as 10%. Because there is no EGR to register as air flow on the MAP sensor, the engine will have to bear the full amount of the enleanment specified in the last table. During steady state operation (say cruising down the interstate), the ECM should be able to use feedback from the O2 sensor to enrich the mixture back to normal. However, as soon as you pull off the interstate and start putt-putting through city traffic (where your RPMs drop and your vacuum increases), the EGR enleanment will be reduced. But the O2 sensor caused enrichment will still be in effect. Thus your engine will run rich until the ECM can learn a new adjustment. So, in summary, you should have periods of reduced power and an overall decrease in fuel economy. I doubt that that is what you wanted.